Overview: There are 10^10 stars in the Milky Way. Thus, if there are 10 barriers to the achievement of technological civilization, each of which independently stops technolife on 90% of all starsystems, we expect only one technological civilization per galaxy.
I call each such barrier a Brick In The Wall: Ten Bricks suffice to wall us off from intelligent life in the Universe.
Can we count to 10? We’ll actually try totting up improbability exponents to base 10, factors, such that if we reach 10, we’re alone in the galaxy. Some of our Bricks are probably wrong — but we’ve probably also overlooked some Bricks in our ignorance. You probably won’t agree with my factors, or even my list of Bricks, so go ahead — come up with your own, add it up, and decide how probable you think technolife in a given galaxy to be.
You need a Solar-class star.
At least 95% of galactic stars are just totally unsuitable — supergiants that live only 100,000 years and sterilize everything around them for light-years, say. And the entire first generation of stars is unsuitable, because they don’t contain any elements but hydrogen and helium — hence their planets can’t be anything but boring gasballs.
Brick factor: 2.0
You need an exquisitely stable star.
The more we study other stars, the more we realize how unusual is our own star. With an orbital lifezone of width 2% or so, evolution of life requires a star with power output stable to a couple of percent — for five billion years straight. This is decidedly Not Normal, even for Solar-class stars.
Brick factor: 0.3
You need a planetary system.
It appears from spin rates of solar-class stars that about half spin quickly, half slowly: The obvious interpretation is that about half have kept their angular momentum, and half put some of it in a planetary system.
Brick factor: 0.3
You need an extraordinarily stable planetary system.
We once thought the Solar system was stable: Newton’s clockwork universe. Recent simulations have shown that in fact the inner solar system is chaotic: Exquisitely small differences in initial conditions cause the positions of the planets to diverge exponentially over time — the inner solar system is inherently unpredictable over significant lengths of time.
We don’t know just what this means for Earthlike-planets, but given the exquisitely tight requirements for the evolution of life, any source of variability on this scale can hardly be anything but bad news.
We are also coming to steadily better understand the resonances and other dynamics of the inner solar system — say, the way Jupiter simply forbids planets from forming in various places, and casually tosses other ones clear out of the solar system — and each improvement in understanding just deepens our appreciation of how lucky we are to be here.
You need nearly circular orbits, to keep a planet in the lifezone for billions of years. Circular orbits appear to be exceptional:
The six planets orbit stars that are similar in size,age, and brightness to the sun and are at distances ranging from 65 to 192 light years from earth. The planets themselves range in mass from slightly smaller to several times larger than the planet Jupiter. They are probably also similar to Jupiter in their compositions–basically giant balls of hydrogen and helium gas, according to researcher Steven Vogt. Their orbits tend to be quite eccentric, tracing oval rather than circular paths. It is beginning to look like neatly stacked, circular orbits such as we see in our own solar system are relatively rare,” said Vogt.
Brick factor: 0.3
You need an earth-like planet.
If you move the Earth’s orbit in or out by about 2%, it either fries or freezes. There’s a very narrow life-friendly belt. Where the inner planets can form is dictated largely by resonances with Jupiter and to a lesser extent other major planets. There is as yet no obvious reason to believe anything but luck put Earth in the lifebelt.
Brick factor: 2.0
You need a Moon-like Moon.
The Earth is really more a double-planet than a conventional planet-moon configuration: The Moon is roughly the same size as the Earth, as astronomic comparisons go. There’s nothing else like it in our solar system, with the arguable exceptions of various asteroids and of Pluto/Charon, itself apparently closer to being a comet or asteroid than a conventional planet.
Without the Moon’s tides to stabilize the Earth’s rotation, there’d be no technolife on the planet: Precession would often lead to the poles pointing away from the Sun and the atmosphere freezing out on the cold side. You wouldn’t wanna live there.
The only way we know of to make the Moon is for something approximately twice the size of Mars to hit the Earth and splash Moon-makings out, without actually shattering the planet. Not a terribly likely scenario.
Brick factor: 2.0
You need an insolation compensator.
Despite the life-zone the Earth orbits in being about 2% wide, the Sun has warmed up by about 30% over the course of the evolution of life on Earth. There is some speculation that feedback loops on the planet accomplish the needed compensation, but to this point none has been convincingly demonstrated: The safest guess at the moment seems to be that we’ve been just plain lucky.
Brick factor: 0.3
You need good stellar neighbors for five billion years.
As the right wing likes to point out, it’s a dangerous universe out there.
It currently appears that most galaxies are quasars on and off, quite possibly sterilizing most of the planets in the galaxy when they turn on. You have to not get toasted by your own galactic core black hole for five billion years straight to produce technolife.
Supernovae go off every century or so in our galaxy, and as one scientist noted, just the neutrino flux will kill every unprotected lifeform for lightyears in all directions. He didn’t specify what would constitute good protection: Since neutrinos will traverse light-years of lead with ease, one may presume most life-forms will be unprotected. Again, you have to have your planet not get toasted every year for five billion consecutive years to produce technolife. That’s fifty million supernovae you have to luckily survive, without a single miss. Go shoot fifty million consecutive free-throws, then come back and continue reading grin. (We won’t even worry about getting killed off by a mere nova.) (See http://www.sciencedaily.com/releases/1999/08/990803073658.htm and http://www.admin.uiuc.edu/NB/99.08/supernovatip.html for evidence of a supernova near-miss about 6 million years ago.)
Galaxies are full of (surprise!) stars. They’re all bobbing up and down in the galactic plane plus diffusing around like a gas. Any close encounter with another star can easily disrupt a planetary system enough to move an Earthtype planet out of the lifezone — and quite possibly out of the Solar System.
Colliding neutron stars are also thought to be bad for children and other living things… enough so to cause mass extinctions every 100Myear or so:
Neutron star could kill us all, but perhaps not today.
As if you didn’t have enough to worry about already, it turns out that we’re 100 million years overdue for mass extinction.
Keep watching the skies if you want some warning. When you see an eerie blue glow, slightly bigger than a full moon, it means that you’ve got just a few days before the apocalypse.
The glow is caused by a burst of gamma rays hitting the upper atmosphere. Following close behind is a high-energy jet of deadly cosmic rays. Once they hit the atmosphere, your chances of survival are not good: researchers believe that the last few times cosmic ray jets hit the Earth, they wiped out up to 95 percent of animal life on the planet.
To get more than a few days warning, you’d have to monitor the orbits of all the nearby neutron star pairs. The collapse and merger of these super-dense balls of matter is the source of the lethal cosmic rays. As the pairs of neutron stars circle around each other, their gravitational pull moves them closer together and spins them faster and faster.
Eventually they collapse into each other and form a black hole, releasing energy as a tightly focused beam of cosmic rays. The beam can travel for up to a million light years before losing its power, so any planet in the line of fire had better watch out.
Any starlight that gets in the way of the cosmic ray jet is kicked out in front of it like a ball; this acceleration pumps the photons up to gamma ray energies and makes them travel faster than the cosmic rays — hence their early arrival at the Earth. Low-intensity gamma ray bursts, thought to be from neutron star mergers in distant galaxies, are detected by astronomers about once a day.
This whole scenario may sound like science fiction, but it’s getting the attention of serious researchers. Calculations of the timings of nearby neutron star collapses show that, just like mass extinctions on Earth, they seem to occur about once every 100 million years. Disturbingly, for the inhabitants of Earth, the evidence suggests the last one probably happened 200 million years ago.
Geological records show there have been five major mass extinctions in the past 500 million years.
Scientists believe the most recent one, which wiped out the dinosaurs 64 million years ago, was caused by the impact of a meteorite. Some 300,000 tons of the element iridium was laid down in the Earth’s crust at this time, and high levels of iridium have also been found in asteroids.
“What caused all the other extinctions is still an open question,” says Arnon Dar, a space physicist at the Israel Institute of Technology. Suggested explanations have included high volcanic activity blocking sunlight and poisoning the atmosphere, and supernova explosions. But there’s no geological evidence for coincident volcanic activity, and supernova explosions don’t occur close enough at a sufficiently high rate.
Dar was the first to suggest that collapsing neutron stars might be to blame. He and his colleagues have studied the likely effects of the cosmic ray jets flung out by neutron star collapses, and their conclusions, to be published next week in the journal Physical Review Letters, make chilling reading.
Cosmic rays are a very serious threat. Entering the Earth’s atmosphere, the jets create showers of lethal high-energy subatomic particles known as muons. As they rain down on the Earth, the muons have enough energy to irradiate and kill almost every living thing in their way.
Dar calculates an “average” muon shower occurrence will give about 100 times the ionizing radiation dose needed for a 50 percent chance of mortality in humans — in other words, enough to kill everyone. Such an intense dose would destroy the central nervous system, causing death within a couple of days.
The cosmic ray burst can last up to a month, during which time muons would also destroy the ozone layer, irradiate the environment and damage vegetation, severing the food chain. Thanks to the Earth’s rotation, and radiation borne on atmospheric winds, the effect would be quickly spread around the globe. The muons also boast massive penetrating power; the radiation can be fatal even hundreds of yards underwater or underground.
“Unlike the other suggested extraterrestrial mechanisms, a lethal burst of atmospheric muons can explain the massive extinctions deep underwater,” says Dar. Suddenly, the fossil record’s reported extinction of marine life, as well as continental life, begins to make sense.
Dar’s doomsday scenario also explains other features of previous mass extinctions that current theories leave to one side. The powerful radiation causes biological mutations that would account for the fast appearance of new species after massive extinctions.
Examination of the fossil record also shows a clear correlation between the extinction pattern of a species and its vulnerability to ionizing radiation.
Insects, for example, have been the great survivors of mass extinctions. According to Dar, this is not surprising as insects can, in general, tolerate up to 20 times the radiation dose that kills most vertebrates. The only time they were severely affected was in the largest mass extinction, 251 million years ago. Even then, only 30 percent of insect species were destroyed, compared with up to 95 percent of other orders of species.
Dar is keen to point out that although things might look bad, being 100 million years overdue for an apocalypse doesn’t make it any more likely to happen today. “The chance of extinction doesn’t increase with passing time,” he says. “The fact that you have not been killed in a car accident so far doesn’t increase the chances of it happening in the next 10 years.”
Looking to assess the actual time we have left, astronomers have examined the orbits of the five pairs of neutron stars observed in our galaxy — it seems that we could have a breathing space of about 50 million years before the first ones collapse.
There’s just one problem, though. The data seem to indicate that our galaxy also contains other neutron star pairs that no one has yet seen. Until we see them, we can’t know when they will merge. So nobody can actually be sure that the apocalypse is not just around the corner.
Brick factor: 1.0
You need good luck with planetary life stressors.
The history of Planet Earth is pockmarked with disasters so big the mess is still clearly visible tens or hundreds of millions of years later. The rock that hit Mexico 65 million years ago knocked down every tree on the planet and killed everything bigger than a rat. (The rats then evolved to fill up the now-empty big-animal niches. That’s us, folks.)
That was far from the worst disaster on record!
The Deccan Traps in India are layers of lava miles deep; The outpouring that produced them was almost unimaginable. Comparing Krakatoa to the Deccan Traps eruption is like comparing a firecracker to an H-bomb.
As far as I can tell, we’ve been just plain lucky with local little planetary disasters like these.
Fewer disasters of this sort, and life might have ambled on indefinitely without producing technolife: Clearly the K/T extinction of the dinosaurs was what opened up room for mammals to diversify and eventually produce us — a little stirring of the pot now and then keeps innovation bubbling.
More disaster of this sort, and life might have been knocked back to the slime stage or worse: A real rain of K/T-scale hits instead of one lone one, or one a couple of orders of magnitude larger, might well have spilled the lifepot into the fire instead of just stirring it. Ditto little events like the Deccan Traps eruption.
Planets that didn’t get as lucky as ours did… don’t wind up producing folks like Homo sap sap.
Brick factor: 1.0
You need a water source.
It has been recently discovered that the Earth is constantly being bombarded with small snowballs. (This is still somewhat controversial, but we have pictures of them hitting, among other things. On the other hand, we don’t see them hitting the Moon, and it seems we should, so the jury is still out on this one.) The amount of water they are calculated to have delivered is about the same as the amount in the oceans. The obvious conclusion is that this is where the oceans came from.
It has also recently been discovered that the outer planets of the Solar System are almost uniquely configured to serve as an efficient conveyer belt forwarding things like small snowballs down from the outer solar system (the only place they can form) to the inner solar system (the only place where warm oceans can exist). So far, at least, this appears to be a quite improbable arrangement, and the most obvious (to me) explanation of why we observe it is the Anthropic Principle: Without that conveyor belt creating oceans on Earth, we wouldn’t be sitting here wondering why it existed.
Brick factor: 1.0
You need about 50/50 water/land ratio.
It isn’t enough to have oceans on Earth: They must also be about 50% of the surface area, in order-of-magnitude terms: we clearly wouldn’t be here if the earth was 1% covered by water, nor if it were 99% covered by water. As usual, there doesn’t appear to be any reason but sheer luck for us having hit the magic life zone on this parameter: We need only glance at Mars to see a world that ran out of water, or look at the amount of land created or flooded by a simple ice age to realize how very fragile the current balance is. A one-kilometer rise or fall in the ocean level would end the story.
Brick factor: 0.3
You maybe need the right weather.
It is most curious that after millions of years of hominid evolution, civilization appeared all over the planet within a period of few centuries: What synchronized them all to 99.99% accuracy?
The obvious answer is the weather. On a whole variety of scales, we live in an absolutely amazing patch of planetary weather. The last year was the warmest year on record; The last decade the warmest decade on record; The last few centuries the warmest and most stable since the last glaciation retreated; The last few millenia possibly the most extraordinarily warm and stable for millions (?) of years; The current glacial period one of the most extraordinarily variable in the history of the planet, so far as we can tell.
Is it pure happenstance that hominids, specializing in adaptability, just happened to evolve and radiate during one of the most climatically variable periods in the history of the planet? Or did that very variability kill off more specialized, less adaptable competitors and open up niches for a family of specializing generalist species?
Is it pure happenstance that technological civilization arose planetwide during an sudden unseasonably (geologically speaking) warm and stable period (even by Earth’s generally extraordinarily warm and stable standards)?
Remember, timing was pretty tight on evolution of technocivilization on Earth: It took five billion years to get from slime to crime, leaving very little margin for error — the planet would have gotten crisped by the Sun in another five billion years. Mess up by a single factor of ten the wrong way, and you lose bigtime. (Given that we spent over two billion years alone just refining the art of slime, that’s pretty scary!)
I’m inclined to believe that it was indeed not at all a matter of chance that our civilizations arose during such an extraordinary climatic period, but that in fact getting very lucky with the weather was a precondition.
Brick factor: 0.3
You maybe need the right continental structure.
(This one is obviously related to the weather Brick, but I don’t think they are actually the same thing.)
The more we study the current world continental formations and atmosphere/ocean interactions, the more we realize how extraordinary they are.
For example, through much of Earth’s history, the landmasses have been gathered in one giant lump sitting more or less horizontally along the equator, with very little tectonic activity, resulting in low to no mountains (no uplift to replace them as fast as weathering tears them down), shallow seas, warm, almost unvarying climate, and presumably simple, stable oceanic circulation patterns in the one big World Ocean.
Today, by contrast, we have a fantastically varigated land and ocean layout.
The main Eurasian landmass and the Americas (which by pure chance?? happen to just barely meet in the middle, keeping the Atlantic and Pacific separate by a few tens of meters vertically and kilometers horizontally — say, 0.1% of the relevant variables) just happen to trap a large north-south ocean between them almost pole-to-pole (how odd, when oceans almost always run east-west and connect globally) which ocean just happens to be bistable, flipping at the drop of a hat between circulation modes which move February temperatures in Europe up or down by 20C.
Meanwhile, on land, an astounding, unprecendented collection of climatic zones has been created, partly because the landmasses just happen to currently reach pole-to-pole, partly because they are so elongated as to produce an amazing amount of coastline (while yet remaining connected into a single global landmass for most biological purposes — humans were able to migrate throughout the planet basically on foot, excepting a few Pacific islands), partly because active tectonics have thrown up towering mountain ranges all over the planet from the Himalayas to the Andes, resulting in a huge collection of climatic zones, both vertically due to precipitation and temperature changes with altitude, and also horizontally due to isolation by mountain ranges, and also climatic modulation by mountain rain shadows and the like.
In short, we appear to live in an era of extraordinarily hypervariable climate in both time and space, both in absolute terms relative to what the planet seems capable of, and also relative to what we know of prior periods in the Earth’s history.
Is it pure coincidence that Homo sapiens sapiens, the consumate adaptor, happened to appear in an era offering more scope for adaptation than perhaps any in the history of the planet? Or was it in fact this hypervariability which suppressed more specialized competitors and drove the evolution of a family of specializing generalist species capable of eventually producing technocivilization?
The Earth is 4.5Gyear old, and it takes about 0.1Gyear to re-arrange the landmasses, so it is far from statistically inevitable that such an extraordinary landmass configuration should pop up at such a convenient time in the evolution of life on this planet.
Brick factor: 0.3
You need a benign interstellar environment.
Yet again, turns out the Earth “just happens” to have veen extra-ordinarily lucky, this time over the last five million years or so, in not having anything around to disrupt the heliopause:
Cosmic Cloud Could Burst Earth’s ‘Breathing Bubble,’ New Computer Simulation Shows
BOSTON, MASS.A colorful new computer animation–created by Gary P. Zank of the Bartol Research Institute at the University of Delaware–shows how even a small cosmic cloud could suddenly burst the “breathing bubble” that protects life on our planet.
The simulation, presented May 28 during the American Geophysical Union’s Spring meeting, also should help guide the spacecraft, Voyager 1 and Voyager 2, through a series of shock waves and a massive “wall” in space nearly two decades from now, says Zank, an associate professor at Bartol and a leading theoretical astrophysicist.
Ongoing studies of Earth’s “cocoon” might someday reveal whether close encounters with cosmic clouds cause periodic extinctions, according to Zank, who earned a National Science Foundation Presidential Young Investigator Award in 1993 and a Zeldovich Medal in 1996.
“We’re surrounded by hot gas,” Zank notes. “As our sun moves through extremely ’empty’ or low-density interstellar space, the solar wind produces a protective bubble –the heliosphere around our solar system, which allows life to flourish on Earth. Unfortunately, we could bump into a small cloud at any time, and we probably won’t see it coming. Without the heliosphere, neutral hydrogen would interact with our atmosphere, possibly producing catastrophic climate changes, while our exposure to deadly cosmic radiation in the form of very high-energy cosmic rays would increase.”
Zank’s startling computer simulations were initially developed to support the Voyager spacecraft, deployed as part of the Voyager Interstellar Mission. Even as the sun rolls freely through wide-open space, he explains, the Earth’s ever-changing bubble generates shock waves and an enormous wall of hydrogen gas. The wall, he says, will sweep past Voyager 1 around 2015–several years later than previously estimated.
Rather like a lung, the heliospheric bubble breathes, but in a highly arythmic fashion, because of an 11-year periodic cycle of solar wind properties. By simulating this breathing bubble, Zank says, he can predict the location of the boundary between the solar wind and the vast interstellar medium of space, which should help the National Aeronautics and Space Administration (NASA) prepare Voyager 1. The battery-operated vehicle is running out of power, Zank notes. To make the most of its instruments, NASA researchers must conserve energy, by switching systems on and off.
Rowdy Space Clouds
Every 66 million years or so, the solar system traces a regular path through the galaxy, oscillating up and down as it sails through “all sorts of environments,” Zank reports. Over the past 5 million years, he says, “We’ve had incredibly smooth sailing” because the sun was lolling through an interstellar medium containing less than one atom per cubic inch of space. That’s empty space, indeed: Even wispy clouds are 100 times more dense. Currently, Zank says, the solar system is in a region of space containing between 3 and 4 particles per cubic inch.
“Space,” Zank notes, “is full of clouds.” One particularly troublesome cloud region, located in a star-forming region towards the Aquila Rift, clearly is headed our way, according to Zank. Pushed by galactic wind, the cloud may collide with Earth’s protective bubble within the next 50,000 years, he says, and some researchers think we could encounter fluffier knots of gas–containing 10 to 100 particles per cubic –> –inch of space–far sooner. Our immediate or local interstellar environment is chock-full of gas clusters known as the Local Fluff, Zank points out, and existing instruments aren’t sensitive enough to detect extremely small clouds. Consequently, Zank says, “We won’t know that our heliosphere is collapsing until we see highly elevated levels of neutral hydrogen and cosmic rays, and a hydrogen wall in the vicinity of the outer planets.”
Did a rogue cloud wipe out the dinosaurs? In 1939, British cosmologist Sir Fred Hoyle suggested that cosmic collisions with clouds may obliterate the heliosphere every now and then. Zank agrees. “The protective solar wind would be extinguished, and cosmic radiation might lead to gene mutations,” he says. “Hydrogen would bombard Earth, producing increased cloud cover, leading perhaps to global warming, or extreme amounts of precipitation and ice ages. We can’t predict every scenario at this point.”
A Bon Voyage for Voyagers 1 and 2?
Using powerful new number-crunching computers at Bartol, as well as systems at national supercomputing centers, Zank created two animations to show the heliosphere in empty space some 5 million years ago, and in a dense cloud containing 10 particles per cubic inch.
In clear space, the sun blows solar wind at supersonic speeds, thereby creating the heliosphere, which Zank describes as “a funny, bullet-shaped bubble.” When the interstellar medium crashes into this bubble, he explains, “it suddenly veers upward and around, like water flowing around a rock in the river.” The result, he says, is a systerm of massive shock waves and a hydrogen wall, which could be 50 times thicker than the distance between the Earth and the sun.
Undisturbed by clouds, the heliosphere appears to take a breath every 11 years, as fluctuations in solar-wind speeds produce a gentle, arhythmic motion, Zank says. Flowing outward, shock waves push the wall and interstellar boundaries farther into space until at last they break and wane, allowing the boundary to contract. This shifting region between the heliosphere and its boundary may filter hydrogen through a process known as “charge exchange,” in which neutral hydrogen and charged particles swap an electron, and so, change identities.
Earth’s protective bubble seems to gasp spasmodically in a dense cloud, so that it collapses and reforms every 331 days, Zank says. The weight of neutral hydrogen, pressing down on the lighter solar wind, “would drive great rollups of instability,” he says. “This well-defined heliosphere structure would disappear and reappear, at times obliterating the hydrogen-filtering region.”
Understanding Cosmic Evolution
Zank’s colorful images aren’t likely to help us avoid a cloud collision, but they may spark a new appreciation for life. On Earth, he says, “These days, and the last 5 to 10 millioin years, have been extremely benign, in an astrophysical sense, and we need to make the most of them, by learning all we can about this cocoon in which we live.” Moreover, Zank says, “We can’t predict our future until we understand our cosmic evolutionary history.”
The new Bartol simulations were obtained by solving an extremely complicated, highly nonlinear system of coupled equations. First, Zank assembled key information about conditions in interstellar space, such as the speed, density and temperature, measured by instruments on the spacecraft, Ulysses, and extrapolated from telescope data. Then, he used that information in his equations, which were fed into computers, along with a second data set describing conditions closer to Earth. Zank’s research was supported by the National Science Foundation and NASA.
Brick factor: 0.3
Summary: How big a Wall?
(We won’t bother worrying about whether a technocivilization survives its first millenium. It appears to have been sheer luck we haven’t nuked ourselves so far, and we’re just opening the bio-war era…) What’s your total? By my counting, that comes to a total brick factor of 11.8: One technocivilization expected per 10^11.8 stars. With 10^10 stars per galaxy, that’s an effective expected rate of one technocivilization per ten to one hundred galaxies, given the softness of the numbers. If I’ve missed any Bricks, we’d expect even less than one technocivilization per galaxy. Since we tend to discover new hazards more frequently than we find that old ones didn’t exist after all, and since we’re still extremely ignorant of much of the process of technolife production, my guess is that we will indeed find more Bricks over time, coming up with an expected technolife density of considerably less than one per galaxy.
I started collecting these on disk (as opposed to in my head) only 98Feb, hence the vagueness of most of the references.
97Jan16 Nature p 234 notes in passing that “The terrestrial planets are thought to have recieved most of their volatiles from bombardment by comets or carbonaceous asteroids.”, footnoting Kass & Young in 1995 Science 268 697-699.
They don’t comment on the planetary conveyor belt in the solar system, but a reasonable conclusion might be that without the conveyor belt, Earth would have much less in the way of volatiles, and perhaps puddles instead of a world ocean, with plausibly disastrous consequences for the development of technological civilization.
The article also notes that compensation for increasing brightness of the parent start over time is needed to keep a planet habitable: They propose that silicate weathering rate on earth is controlled by temperature and serves this function, and that this requires significant exposed land on the planet together with plate tectonic action to recycle CO2 from the seabed into the atmosphere, and guess that the desolation on Mars is due to the lack of plate tectonics to keep this mechanism going.
http://www.abc.net.au/science/news/stories/s46071.htm on 99Aug30 quotes Tokyo Institute of Technology researchers as concluding that plate tectonics absorb a gigaton of water per year but release only a fifth that much, and that consequenty the ocean may be gone in a billion years. If that holds up, it seems to implies one needs enough some plate tectonic activity but not too much, else the ocean may go before technolife can evolve.
Main point of the article is to argue that moons around gas giants might be habitable — specifically, that a 0.12 earthmass moon with an Io-like orbital resonance to heat it and a Ganymede-like magnetic shield to protect its atmosphere might be habitable for billions of years if the solar constant was appropriate.
All by way of hoping for life on the extrasolar planets found to date, which are all gross gasbags
Very empty article, but they seem to be implying that neutron star collisions happen often enough to cause mass extinctions every 100M years or so throughout the galaxy: It may be that this is enough to weed out a lot of potential techlife candidate planets?
Star collision killed dinosaurs — Israeli
JERUSALEM (AP) — Israeli scientists have a new
theory on why the dinosaurs became extinct:
cosmic radiation that bombarded the Earth
following the collision of two neutron stars.
Physicists from the Space Research Institute at
the Technion University in Haifa theorize that the
mass extinction 65 million years ago was
by the merging of twin stars near the Earth inside
the Milky Way galaxy.
This collision created a deadly wave of cosmic
radiation that destroyed the protective layers of
the Earth’s atmosphere, frying vegetation and
obliterating most animal life, the researchers say.
There have been several theories that astral
radiation caused mass extinctions.
David N. Schramm, an astrophysicist at the
University of Chicago, suggested last year that
exploding stars called supernovas could have
caused another mass extinction — the most severe in
Earth’s history — that killed 95 per cent of
all life 225 million years ago.
But Arnon Dar, a physics professor at Technion
University, said supernovas could not have
caused all six mass extinctions that swept
the Earth in the last 650 million years — one about
every 100 million years.
“The rate of supernova explosion is not great
enough to explain the 100-million-year extinctions,”
Dar said. “But the merging of neutron stars
could be responsible.”
Twin stars merge every day somewhere in the
galaxy, producing radiation in the form of gamma
and cosmic rays that strike the Earth’s
atmosphere. Usually, the stars are too far away to do any
damage and the radiation is harmlessly
by the ozone layer.
The dinosaurs’ demise has been the subject of
hot debate in scientific circles. Dar discounts the
prevailing theory — supported by Schramm —
that an asteroid strike was to blame.
Dar said this theory does not explain the great
leap in biodiversity following the mass extinctions.
He contends the vast amount of radiation
produced by a neutron star collision explains why the
number of animal and plant species increased
quickly after mass extinctions.
Those animals that survived — because of their
hardiness or lack of radioactive exposure —
would have produced a greater number of
mutations, Dar said.
Both Schramm and the Israeli scientists are
continuing to look for evidence of irradiated minerals
in the Earth’s geologic layers, signs of
a supernova or neutron star collision.
“I think the real test will be if we can find
these isotopic anomalies,” Schramm said. “Unless we
find those, we’re missing the smoking gun.”
Good week for me in science news :). The life on mars case appears
to be weakening, which makes life easier for me, and you remember
my passing on the report that the solar system outer planets are
uniquely configured to efficiently transport outer solar system
comets into the inner solar system, and that this would only make
sense if they were contributing something important to life on
earth, like the oceans:
Cosmic snowballs may have seeded Earth
Copyright ) 1997 Nando.net
Copyright ) 1997 Reuter Information Service
WASHINGTON (May 28, 1997 8:25 p.m. EDT) – Giant cosmic snowballs are
bombarding the upper atmosphere, then
breaking up, adding water to Earth’s oceans and possibly nurturing
on the planet, scientists reported on Wednesday.
The snowballs are actually small comets about 40 feet in diameter,
appear to be streaking toward Earth in a steady
However, according to data provided by NASA’s Polar satellite, the
snowballs are no danger to people on Earth or to
astronauts, spacecraft or airplanes because they break up at altitudes
from 600 miles to 15,000 miles.
At that height, the snowballs break up first into fragments and then
exposure to sunlight vaporizes the fragments into vast
clouds which are in turn dispersed by winds.
These cometary clouds eventually blend with normal weather systems and
cosmic rain mixes with the common variety,
according to Louis Frank of the University of Iowa, who first
about the phenomenon in 1986.
“This relatively gentle ‘cosmic rain’ — which possibly contains
simple organic compounds — may well have nurtured the development of
life on our planet,” Frank said in a statement.
Earthly life might have developed from the tiny amounts of organic
material contained in the dust of these small comets, Frank
said later in a telephone interview.
“One of the things that scientists are going to want almost
is to find out how much organic material is in these
objects,” Frank said.
The ice in the small comets may have been shielded by a carbon crust,
even by a kind of “natural saran wrap” so that it can
survive entry into the atmosphere, Frank said.
The cosmic rain from these small comets accounts for only about one
ten-thousandth of an inch of water on Earth each year,
scientists from the National Aeronautics and Space Administration
But Frank said that over the course of billions of years, even this
miniscule amount of water would be enough to fill all of
The Polar satellite, which orbits high above the Arctic Circle,
the snowballs as they disintegrated, and using a filter
that detects visible light emitted by water molecules, Frank
that the snowballs consist mainly of water.
Scientists have long believed that regular-sized comets, such as this
year’s clearly visible Comet Hale-Bopp, are made up
largely of water ice and cosmic dust.
The finding that these mini-comets also contain water and that they
are headed for Earth at a furious rate — possibly thousands each day
— bolster Frank’s earlier theory about the cause of what appeared to
be holes in the atmosphere.
Frank theorized in 1986 that these apparent holes were caused by the
disintegration of small comets in the upper atmosphere,
but many colleagues discounted the theory and attributed the apparent
holes to an instrumental problem.
Frank’s findings were presented on Wednesday at a meeting of the
American Geophysical Union in Baltimore.
Another brick in the wall? Earth getting hit by something Mars-size
surviving was already a big brick in the wall: Now the impactor is
times the size of Mars. Yow!
Study says moon formed by collision with giant
Copyright ) 1997 Nando.net
Copyright ) 1997 Agence France-Presse
WASHINGTON (July 28, 1997 12:15 p.m. EDT) – The moon may have been
formed billions of years ago by a
collision between the Earth and a giant planet three times the size of
Mars, a study said Monday.
The study released by the American Astronomical Society said the
collision with a “rogue planet” may have
vaporized enough material from the Earth’s upper layers to form the
University of Colorado researchers based their research on analysis of
rocks brought back from Apollo space
missions to the moon.
While many scientists have accepted this collision theory, the new
indicates the impact to create the moon
would have required a far bigger object than previously believed.
“This was a surprising result … our calculations indicate a lot more
impact energy than previously believed would
have been required to produce enough material to form the moon,” said
researcher Robin Canup.
The study suggests the planet sideswiped the Earth some 4.5 billion
years ago while the Earth was still malleable.
The impact vaporized upper portions of the Earth’s crust and mantle,
spraying the material into orbit. The material
subsequently spread into a gaseous disk and then formed hot “moonlets”
that eventually coalesced into the single
moon we see today, the study said.
“Large-scale impacts like this one probably played a crucial role in
shaping the solar system,” Canup said. “We
believe this theory is a linchpin to understanding how planets formed
our solar system and in solar systems that
may exist around other stars.”
On the Another Brick In The Wall front, I presume you noticed that
Nature reports that the latest computer simulations indicate that
producing the Earth’s moon requires Earth to be hit by a body more
like double Mars-mass, rather than the roughly-Mars-mass previously
postulated, and that this significantly drops the probability of
finding Earth-Moon like systems elsewhere. On the downside, they
still can’t find a way to get rid of the angular momentum from that
scenario: It would be -really- spectacular if it turned out that you
can only form Earth-Moon via a three-body interaction more improbable
yet :). I’m not going to predict that, however: My sense is that I/we
already have enough bricks in the wall to explain why we’re alone in
the galaxy, meaning that I/we can’t legitimately predict discovery of
further improbabilities based just on us being here and apparently
Comets not the Earth’s oceans only source of
Copyright ) 1998 Nando.net
Copyright ) 1998 Agence France-Presse
WASHINGTON (February 5, 1998 4:55 p.m. EST http://www.nando.net) – The
composition of the Hale-Bopp comet’s tail appears to contradict
comets were the single source of water filling Earth’s oceans, the
Astronomers have long considered comets a sort of fossil evidence of
solar system was formed.
And some have believed that the ice, dust and rocks in comet tails may
played a crucial role in the formation of the atmosphere of the
Earth’s oceans with water and setting the stage for life to develop.
Now astronomers at the University of Honolulu in Hawaii and at a Paris
observatory say that they have found HDO — water in which one –>
atom is replaced with deuterium — in the ice of the Hale-Bopp comet.
Similar findings were made with the Halley and Hyakatuke comets.
But the authors of this study found that the proportion of this heavy
HDO, is considerably higher in the comet tails than in the Earth’s
“It appears that comets by themselves cannot be the only source of
Earth’s oceans,” the authors concluded.
One more thing that can go wrong building an Earth:
New Model Explains Venusian Land Forms
Because Earth and Venus have nearly the same size, scientists long
have called them planetary twins.
But scientists theorize the processes that form the geological
features of the planets are different. Earth forms its continents and
physical features and sheds its interior heat by plate
tectonics. Though Venus might be expected to do the same, its surface
shows scant evidence for plate tectonics, and planetary researchers
long have debated, often heatedly, just what the corresponding process
is on our sister planet.
Now a new model of Venus, derived largely from the highly successful
Magellan Mission early in this decade, shows that two of the planet’s
most predominant features, crustal plateaus and volcanic rises, were
formed by a mechanism similar to hot spot plumes, a process still
active on Earth today and evident in the Hawaiian Islands. Hotspots
are thermal plumes of hot rock originating deep within the Earth and
rising buoyantly upward over millions of years. They eventually
surface in dramatic, lava-spewing displays geologists call flood
The new interpretation comes from the mapping of very subtle
geological faults on the surfaces of the crustal plateaus, and was
published March 6, 1998, in Science magazine.
Roger J. Phillips, Ph.D., professor of earth and planetary sciences at
Washington University in St. Louis, and his colleague Vicki L. Hansen,
Ph.D., professor of geological sciences at Southern Methodist
University in Dallas, analyzed recent data and hypothesize that a
thickening of the Venusian lithosphere, the outer strong shell of a
rocky planet , approximately one billion years ago largely shut down
the creation of crustal plateaus and led to the formation of volcanic
Phillips and Hansen suggest that the thickening occurred rapidly in
geological time, in 100 to 200 million years. The thickening prevented
the plumes from melting substantially and creating new crustal
material to form crustal plateaus. Volcanic rises form when there is
not massive melting in the plumes.
Phillips and Hansen estimate the Venusian lithosphere is about 60
miles thick today, compared with about 24 miles thick at the end of
the ‘thin lid’ era, which they suggest lasted up until about one
billion years ago.
“To maintain the thin lithosphere you have to have some sort of
recycling going on, which on Earth is plate tectonics, but that’s not
the case with Venus over the past billion years,” said Phillips. “Our
calculations also show that you get plenty of plains volcanism during
the thin lid era, almost an embarrassment of riches, with formation
going on almost constantly up to the point where the lithosphere
That conclusion clashes with another popular planetary theory that
holds that plains formation was an abrupt episode on Venus.
Phillips said the lack of water on Venus no doubt contributed to the
formation of the thickened lithosphere.
“The rocks are stronger on Venus probably because of a lack of water,”
he said. ” It probably got to the point where the stresses induced by
the interior just couldn’t break the strong rocks, and the process of
lithospheric recycling, which maintained the thin lid, just quit.
“Water is the basic di fference between Venus and Earth in this
context Water makes the lithosphere of Earth relatively weak, and lack
of water makes this structure relatively strong on Venus. Whether you
have recycling of the lithosphere into the mantle comes down to a
competition between how strong the lithosphere is and how much force
from the convecting mantle can be applied to break the
lithosphere. This competition basically operates differently on the
Because the Phillips and Hansen model indicates a recycling process
during the thin lid era, it’s conceivable that Venus was using plate
tectonics during its geological heyday.
“Prior to the thickening of the lithosphere, Venus could have had
plate tectonics, as far as we’re concerned,” Phillips said. “There was
some kind of lithospheric recycling. It may have been plate tectonics
or something else, but it was there.”
The model also couples the climate and interior evolution of Venus,
the planet that suffers from the runaway greenhouse effect to give a
present-day surface temperature of nearly 900 degrees Fahrenheit.. All
of the volcanism that went on during the early years of the planet
pumped so-called greenhouse gases sulfur dioxide and carbon dioxide in
the Venusian atmosphere, so that the surface temperature was even
“The gases increased the greenhouse effect, which in turn raised
surface temperatures, and that in turn led to more interior melting,
which resulted in more greenhouse gases being released,” Phillips
said. “There is a very tight coupling between climate evolution and
interior evolution on Venus over much of its history, and that is
something we’re just beginning to take seriously on Earth.
Here’s another brick: superflares:
Thursday January 7 1:03 AM ET
New Space Fear Killer Superflares On Sun-Like Stars
By Deborah Zabarenko
AUSTIN (Reuters) – Armageddon on some distant planet might not come with a bang. Instead, it might
come as a superflare.
Monster flares of energy emitted by stars very much like our sun would warm neighboring planets, fry
satellites and destroy any Earth-like life, starting at the bottom of the food chain and working up,
astronomers said Wednesday.
The good news? It won’t happen here.
It may already have occurred on nine sun-like stars — three of them virtually identical to our sun — where
such superflares have been detected, according to Bradley Schaefer of Yale University.
Superflares are exponentially more powerful than the solar flares ejected by our sun, Schaefer said at a news
conference at a meeting of the American Astronomical Society.
Regular solar flares can knock out power grids and communication satellites, but lack the energy to cause
long-term disaster on Earth.
By contrast, superflares are as much as 10 million times as energetic as regular solar flares. The evidence that
they occur on stars similar to our sun was deemed “troubling” by Schaefer but he acknowledged that our sun
is a poor candidate for the deadly, once-a-century superflare.
There are no records of recognized superflares on Earth in the last 150 years and this phenomenon definitely
would have been recognized: the sun would have glowed brightly, there would have been a short, intense heat
wave and an aurora — like the Northern and Southern Lights — that would have stretched all the way to the
Beyond that, there is no evidence of a flood on Saturn’s icy moons for the last billion years or so and
superflares would have melted these icy oceans which would then have refrozen into visible flood plains.
Our sun also lacks what appears to be a key trait of a superflare star: a nearby big planet like Jupiter that would
have enough of a magnetic field to spark a flare.
To do so, the Jupiter-like planet would need to be as close to the sun as Mercury.
Still, if our sun produced a huge superflare, the consequences would be catastrophic. First, all satellites would
quickly burn up and the blast would break up the ionosphere to prevent long-distance radio transmission.
The blast would soon deplete the ozone layer that shields Earth from deadly ultra-violet radiation. In essence,
the ozone hole that has been observed over the South Pole would extend over most of the planet and last for a
year or more.
That would mean quick death for tiny organisms at the bottom of the food chain, like ocean-dwelling
plankton. It also would scorch food crops like wheat and corn.
Schaefer stressed, however, that this is not going to happen on Earth and that the superflare stars which have
been detected are too far away to do any damage here.
1999Jun23 Here’s two more bricks: Unusualness of the sun. http://exosci.com/news/165.html
Our exceptional sun
Don’t believe everything you read in books-our Sun is no ordinary
star. And its very uniqueness has implications for SETI, the search
for extraterrestrial life, claims Guillermo Gonzalez of the University
of Washington in Seattle: “Unless astronomers narrow down their search
to stars as exceptional as the Sun, they are wasting much of their
The Sun is a single star whereas most stars are in multiple
systems. But that apart, textbooks say the Sun is pretty
average. However, after trawling through the data on the Sun, Gonzalez
has found many idiosyncrasies. It is among the most massive 10 per
cent of stars in its neighbourhood. It also has 50 per cent more heavy
elements than other stars of its age and type, and about a third of
the variation in brightness.
The most unusual aspects of the Sun concern its orbit around the
centre of the Galaxy, says Gonzalez. Its orbit is significantly less
elliptical than that of other stars of its age and type, and hardly
inclined at all to the Galactic plane. What’s more, the Sun is
orbiting very close to the “corotation radius” for the Galaxy-the
place at which the angular speed of the spiral pattern matches that of
Gonzalez argues that these exceptional characteristics made it
possible for intelligent life to emerge on Earth. He points out that
stable planetary orbits such as the Earth’s are much more likely
around single stars like the Sun. For a massive star with inhabitable
planets that are relatively far away, stellar flare-ups would be
little threat to the planets. Heavy elements are essential to make
planets like Earth, and a star with a stable light output is essential
As for the orbit of the Sun, its circularity prevents it plunging into
the inner Galaxy where life-threatening supernovae are more
common. And its small inclination to the Galactic plane prevents
abrupt crossings of the plane that would stir up the Sun’s Oort Cloud
and bombard the Earth with comets. By being near the Galaxy’s
corotation radius, the Sun avoids crossing the spiral arms too often,
an event that would expose it to supernovae, which are more common
Because life-bearing stars have to be close to the corotation radius,
that rules out more than 95 per cent of stars in the Galaxy in one
fell swoop. “There are fewer stars suitable for intelligent life than
people realise,” says Gonzalez, who has submitted his findings to
Astronomy & Geophysics. “I’m amazed at how little thought the SETI
people put into selecting their stars.”
Seth Shostak of the SETI Institute in Mountain View, California,
disagrees. “Our targets are all very close to the Sun. They share our
Galactic neighbourhood and motions. If the Sun is the most suitable
type of star to be scrutinised, then we are, indeed, looking in all
the best places.”
“Most astronomers disagree with Gonzalez,” adds SETI researcher Dan
Werthimer of the University of California at Berkeley. “Our Sun is
pretty average. In any case, you don’t need a star exactly like our
Sun for life.”
Primordial leaks in South Australia Friday, 24 September 1999 Primordial gases from the days of Earth’s formation found seeping out of the ground at gas wells in South Australia and south western US have undermined current theories about how the atmosphere was formed. Writing in this week’s Science, Caffee et al. analyzed the concentration of different isotopes of xenon in the gas from these wells and found that the isotopic “signature” is different from that of xenon in the atmosphere, although it is similar to that of xenon in meteorites. Scientists have previously proposed that the Earth’s present atmosphere was formed from degassing of the planet, but the mismatch between the atmospheric and xenon found in the mantle below the Earth’s crust calls this idea into question. “It can’t be as simple as we’ve thought,” co-researcher Professor Alan Chivas from the University of Wollongong’s Geosciences Department told The Lab. “We now need to come up with a more complex hypothesis as to how the atmosphere was formed.” The researchers report that the xenon seems to be coming from a reservoir deep within the Earth that contains non-reactive gases that have remained relatively unchanged since the Earth formed from a massive disk of dust and gas that was the solar nebula. They say the reservoir has probably stayed pristine because it has been isolated from the mixing processes in the convecting mantle below the Earth’s crust.
Here’s a researcher reporting that the livable period on earth is 90% over, suggesting that technolife just barely squeaked in under the wire:
BBC Homepagelow graphics version | feedback | help
BBC News Online
You are in: Sci/Tech: Specials: Washington 2000
Sunday, 20 February, 2000, 16:51 GMT
Date set for desert Earth
Mars Mars: Will Earth look like this?
By BBC News Online’s Damian Carrington in Washington DC
The Earth is entering the final 10% of its lifespan, according to a US meteorologist.
Dr James Kasting, at Penn State University, calculates that the Earth’s oceans will disappear in about one billion years’ time, due to increased temperatures from a brightening Sun.
Mass – 1.99e30 kg
Mass consumption/year – 10e17 kg
Current age – 4.5e9 years
Hydrogen-fuelled Life left – 10e10 years
However, well before the planet is left as an arid desert, the level of carbon dioxide in the atmosphere will be too low to support plant life, destroying the foundation of the food chains.
“The Sun, like all main sequence stars, is getting brighter with time and eventually temperatures will become high enough so that the oceans evaporate,” said Dr Kasting.
At 60 degrees Celsius (140 degrees Fahrenheit), water becomes a major constituent of the atmosphere. Much of this water drifts up to the stratosphere and is lost into space. Eventually, all the oceans will leak out of the Earth’s grasp.
“Astronomers always knew that the oceans would evaporate, but they typically thought it would occur only when the Sun left the main sequence – that will be in five billion years.”
Sun The Sun will consume Mercury
Stars leave the main sequence when they stop burning hydrogen. The Sun will then become a red giant, swamping and obliterating Mercury. Venus will lose its atmosphere and become a burnt-out planet.
“However, my calculations show the oceans may evaporate much earlier,” said Dr Kasting. “They are somewhat pessimistic and present a worst-case scenario, but they say a billion years.”
The earlier loss of carbon dioxide will occur because as the climate gets hotter and wetter, more rock is weathered by rain. This dissolves carbon dioxide and hides it away on the ocean floor as calcium carbonate.
“Obviously, a billion, even a half billion years, is a long way off in the future,” said Dr Kasting. “But these models can help us refine our understanding of the time that a planet remains in an orbit where life can exist.”
“If we calculated correctly, Earth has been habitable for 4.5 billion years and only has a half billion years left.”
Dr Kasting’s comments were made at the annual meeting of the American Association for the Advancement of Science.
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20 Feb 00 | Washington 2000
Into a new millennium of science
08 Sep 99 | Sci/Tech
Leaking Earth could run dry
04 Oct 99 | Sci/Tech
Hopes of Mars oceans dry up
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We apparently got very lucky with the K-T boundary hit:
Asteroid Devastation Could Even Be Worse Than Feared
CORVALLIS, Ore. – Researchers say in a new report that if a huge
asteroid were to hit the Earth, the catastrophic destruction it
causes, and even the “impact winter” that follows, might only be a
prelude to a different, but very deadly phase that starts later on.
They’re calling it, “ultraviolet spring.”
In an analysis of the secondary ecological repercussions of a major
asteroid impact, scientists from Oregon State University and the
British Antarctic Survey have outlined some of the residual effects of
ozone depletion, acid rain and increased levels o f harmful
ultraviolet radiation. The results were just published in the journal
The findings are frightening. As a number of popular movies have
illustrated in recent years, a big asteroid or comet impact would in
fact produce enormous devastation, huge tidal waves, and a global dust
cloud that would block the sun and choke the plane t in icy,
winter-like conditions for months. Many experts believe such
conditions existed on Earth following an impact around the
Cretaceous-Tertiary, or K-T boundary, when there was a massive
extinction of many animals, including the dinosaurs.
That’s pretty bad. But according to Andrew Blaustein, a professor of
zoology at Oregon State University, there’s more to the story.
“Scientists have pretty well documented the immediate destruction of
an asteroid impact and even the impact winter which its dust cloud
would create,” Blaustein said. “But our study suggests that’s just the
beginning of the ecological disaster, not the e nd of it.”
Blaustein and colleague Charles Cockell examined an asteroid impact of
a magnitude similar to the one that occurred around the K-T boundary,
which is believed to have hit off the Yucatan Peninsula with a force
of almost one trillion megatons.
The immediate results would be catastrophic destruction and an impact
winter, with widespread death of plants and the large terrestrial
animals – including humans – that most directly depend on those plants
for food. That’s the beginning of an ugly scena rio, the researchers
As a result of the impact, the atmosphere would become loaded with
nitric oxide, causing massive amounts of acid rain. As they become
acidified, the lakes and rivers would have reduced amounts of
dissolved organic carbons, which would allow much greater p enetration
of ultraviolet light.
At first, of course, the ultraviolet rays would be blocked by the dust
cloud, which sets the stage for a greater disaster later on. Many
animals depend on some exposure to ultraviolet light to keep
operational their biological protective mechanisms agains t it –
without any such light, those protective mechanisms would be eroded or
During the extended winter, animals across the biological spectrum
would become weaker, starved and more vulnerable. Many would die. Then
comes ultraviolet spring, shining down on surviving plants and animals
that have lost their resistance to ultraviolet radiation and
penetrating more deeply, with greater intensity, into shallow waters
than it ever has before.
“By our calculations, the dust cloud would shield the Earth from
ultraviolet light for would cause levels of ultraviolet radiation to
at least double, about 600 days after impact.”
According t photosyntheto stress here is that with an asteroid
collision, there will be many synergistic effects on the environment
that go far beyond the initial impact,” said Cockell, a researcher
with the British Antarctic Survey who did some of th is analysis while
formerly working with NASA. “Effects such as acid rain, fires, the
dust clouds, cold temperatures, ozone depletion and ultraviolet
radiation could all build upon each other.”
During the K-T event, the scientists said, many of the animals may
actually have been spared most of the ultraviolet spring they
envision. That impact, oddly enough, hit a portion of the Earth’s
crust that was rich in anhydrite rocks. This produced a 12-y ear
sulfate haze that blocked much of the ultraviolet radiation. But it
was a lucky shot – that type of rock covers less than 1 percent of the
So when the next “big one” comes, the scientists said, the ecological
repercussions may be more savage than any of those known in Earth’s
long history. The collision will be devastating, the “impact winter”
But it will be the ultraviolet spring that helps finish off the
Sounds like we’re a bit lucky our beast isn’t feeding:
Astronomers Discover “Feeding” Mechanism For Black Holes
COLUMBUS, Ohio — Astronomers at Ohio State University used an
innovative imaging technique to discover swirling masses of
interstellar dust spiraling into the center of nearby galaxies.
The researchers believe this interstellar dust is feeding supermassive
Despite mounting circumstantial evidence that black holes occupy the
heart of most galaxies, astronomers haven’t seen compelling evidence
of the material that might “feed” those black holes until now. Their
study appeared in a recent issue of the Astronomical Journal.
Using NASA’s Hubble Space Telescope, Richard Pogge, associate
professor of astronomy, and Paul Martini, astronomy graduate student,
devised a plan to point two cameras — one that records visible light
and one that records infrared — at nearby galaxies that may contain
supermassive black holes. They combined infrared and visible-light
images to create single images of the interstellar dust clouds in the
centers of these galaxies.
“Imagine if we could take a picture that showed only the dust in a
galaxy,” said Pogge. “We can’t exactly do that, but we can get pretty
The Hubble telescope enabled the Ohio State astronomers to zero in on
the very center of 24 nearby spiral-shaped galaxies with extremely
bright centers. Astronomers believe the centers of these galaxies are
bright because they contain active supermassive black holes consuming
matter from their surrounding galaxies.
Astronomers call a black hole “active” when its powerful gravity tears
material apart, releasing radiation and brightening the galaxy’s
center. Only 1 percent of galaxies that should contain supermassive
black holes appear to be in an active state.
Most pictures of these active galaxies show the giant arms of gas and
dust that give spiral galaxies their shape. Pogge and Martini focussed
instead on only the central 1,000 light years — approximately 1
percent of the total diameter of these galaxies.
“We looked at a region people were unable to study before,” said
Within 20 of the 24 galaxies they photographed, they saw a secondary,
mini-spiral of dust that appeared to go directly into the center where
the supermassive black hole resides.
These “nuclear spirals” may be the feeding mechanism that activates
black holes, Pogge and Martini said.
Black holes like the one in our own Milky Way may be inactive, Pogge
said, because they aren’t receiving any nourishment from their host
“Before black holes become active, you have to feed them,” Pogge said.
And supermassive black holes have voracious appetites. Astronomers
calculate that black holes must consume stars, gas, or dust in amounts
up to the mass of our sun every year to remain active.
Martini explained that over time the material in an inactive galaxy
may reach an equilibrium in which it orbits the central black hole at
a distance just out of the hole’s reach. The black hole wouldn’t
receive any fuel, he said, until some kind of disturbance triggered an
avalanche of material into the center.
The disturbance could come in the form of a collision with ano
propagate and have a very large effect.”
Pogge and Martini think the nuclear spirals form when material
orbiting near the centers of , Pogge, Msse galaxies lack the
mini-spiral structures seen in their brighter cousins.
This one looks significant, but I’ve no clue what to conclude:
Meteoroid Bombardment Of Moon Has Intensified In Past 500 Million
Years, Coinciding With Blossoming Of Life On Earth
BERKELEY (3/9/00) — A new chronology of meteoroid impacts on the moon
shows some surprising correlations with major biological events on
By dating minute glass beads thrown out by impacts over the millennia,
scientists at the University of California, Berkeley, and the Berkeley
Geochronology Center have not only confirmed expected intense meteor
activity 4 to 3.5 billion years ago, when the large lunar seas or
maria were formed, but have discovered another peak of activity that
began 500 million years ago and continues today.
The tapering off of the first peak of activity, which probably
included many large comets and asteroids, coincides with the earliest
know evidence of life on Earth. The second and ongoing peak, which
from the evidence seems to have been mostly smaller debris, began
around the time of the great explosion of life known as the Cambrian.
“The first life on Earth arose just after this real crescendo around
3.5 billion years ago,” said Paul R. Renne, adjunct professor of
geology and geophysics at UC Berkeley and director of the Berkeley
Geochronology Center. “Maybe life began on Earth many times, but the
meteors only stopped wiping it out about 3 billion years ago.”
The more recent and ongoing activity is even more intriguing.
“It’s not surprising that the impacts tapered off about 3 billion
years ago. The solar system was just getting cleaned up, primarily by
Jupiter and the Sun,” said Richard A. Muller, a professor of physics
at UC Berkeley and a research physicist at Lawrence Berkeley National
Laboratory. “What is surprising is the reversion from a benign to a
violent solar system about 500 million years ago.
“This work opens up a new field that tells us something about the
history of our solar system that was totally unanticipated. Until now
we did not realize how peculiar the past 500 million years has been.”
UC Berkeley graduate student Timothy S. Culler, along with Renne,
Muller and Timothy A. Becker, laboratory manager at the Berkeley
Geochronology Center, report their findings in the March 10 issue of
the journal Science.
Though all the Berkeley researchers agree on the new impact chronology
for the moon, they have their own ideas about its implications.
Renne, for example, leans toward the theory that interstellar dust
seeded the Earth with organic molecules, from water to amino acids,
that were incorporated into life on Earth during the past 500 million
“Life already here would suddenly have a new stimulus, a greater need
to evolve quickly and more raw material to do it,” Renne
said. “Impacts would have to be really, really big and really, really
frequent to be deleterious to life on Earth, and it’s clear that the
flux over the past 500 million years has been relatively small
objects. We don’t see a lot of young large craters on the moon. We’ve
come to accept the idea that impacts are strictly bad news for life on
Earth, but now that’s not so clear.”
Culler, the graduate student who originated the project under the
supervision of Muller and Renne, sees the intense meteor activity as
evidence that large meteor impacts played a major role in the
evolution and extinction of life.
“It shows that large impacts may have been more frequent in the last
500 million years, creating more extinctions, like the comet or
asteroid that wiped out the dinosaurs 65 million years ago, ” Culler
said. “Even a number of smaller impacts can have a disastrous effect
on the atmosphere and cause mass extinctions.”
Muller too emphasizes the role impacts have played in the history of
life on Earth. It’s not surprising that the recent intense period of
meteor activity coincides with the rapid radiation of life on Earth,
“We’re only beginning to realize the role played by catastrophe in the
evolution of life,” he said. “When it comes to survival of the
fittest, it’s not only the ability to compete with other species that
counts, but also the ability to survive occasional catastrophe. That
requires complexity and flexibility.”
Muller has proposed several controversial theories about the solar
system, including that the sun has an unseen companion star, one he
calls Nemesis, that orbits the sun every 26 million years and
periodically knocks comets out of their orbits, sending them hurtling
toward the inner solar system. He also has proposed that periodic
climate changes are the result of the Earth’s orbit periodically
tilting up out of the orbital plane of the planets and intersecting a
cloud of dust, debris and meteoroids.
The current research was suggested by Muller in 1991, in part as a way
to determine whether the moon’s impact record shows evidence of a 26
million-year cycle. Muller hit upon the idea of argon-40/argon-39
dating of lunar spherules as a way to get a more precise chronology of
the intensity of bombardment of the moon and, by implication, the
“I realized that we didn’t have to go to the individual craters in
order to determine their age, because the craters sent samples to us,”
Muller said. “We could obtain samples of hundreds of different craters
from just one location, without having the expense of going back to
the moon. This idea is likely to open up a completely new round of
Spherules are mostly basaltic glass, Culler said, created when a
meteor hits the surface and generates intense heat that melts the rock
and splatters it outward. As droplets of molten rock fall back to the
surface they quickly cool to form a glass, much like obsidian.
Culler, Becker and Renne analyzed 155 beads from one gram of lunar
soil picked up in 1971 by Apollo 14 from the Fra Mauro formation – a
lunar highland bordering Mare Imbrium. The mineral composition of each
bead was determined with a microprobe before it was laser melted and
the argon gas captured for isotopic analysis.
Contrary to assumptions, they found that the cratering rate on the
moon has not been constant over its history. Approximately twice as
many impacts occurred between 4 and 3 billion years ago as occurred
between 2 and 1/2 billion years ago. About 500 million years ago the
intensity of impacts increased nearly to what it was at the peak of
activity 3.2 billion years ago.
Though the dating method was not sensitive enough to reveal a 26
million-year cycle in th For the future, Renne says, it is “critical
to launch new lunar sampling missions targeted to areas rich in
potassium,” in order to confirm the results and probe further back
into the moon’s history.
The project was funded by the Ann and Gordon Getty Foundation, through
the Berkeley Geochronology Center and Richard Muller. NASA provided
the lunar samples.
From ionus@… Fri Mar 31 18:12:07 2000
Subject: unusual solar composition brick
Did we already discuss the apparent fact that the sun is 50-100%
richer in metals than ‘average’ stars its age? I forget where this
info comes from, but I’ve seen it cited as a well-established fact. If
that’s the case, it certainly is another ‘order of magnitude’ reducer
in the complex life equation, since a metal-rich protostellar nebula
is pretty clearly essential to the formation of earthlike planets.
The Radio Ionus News Service of Earth
(The 2000Jul Scientific American also notes that the Sun is
Physics News Update
The American Institute of Physics Bulletin of Physics News
Number 491, June 29, 2000, 2000 by Phillip F. Schewe and Ben Stein
A Hofstra-Williams-Colgate-Manchester (UK) team of astronomers have
the National Radio Astronomy Observatory 12-m radio telescope to scan
a huge molecular cloud only 30 light years from the
In particular they look at the spectra of hydrogen cyanide (HCN) and
its deuterium counterpart DCN. In general stars are
expected to be net consumers (not producers) of deuterium: they burn
it into helium. But the galactic center is the Times Square of
the Milky Way; it is the scene of jets, bursts, x-ray and gamma
sources, a massive black hole, filaments, arcs, and other
From their observed ratio of deuterium-to-hydrogen D/H, the
researchers (Don Lubowich, Jay Pasachoff, Tom Balonek, and Tom
Millar) deduce three things: (1) The D/H ratio is higher than you
would expect in the absence of a source of virginal unprocessed
material (high in D, low in heavier elements). This demonstrates that
matter comparatively rich in D is indeed raining down with
the cloud onto the plane of our galaxy (see figure at Physics News
Graphics). In other words, the infalling matter is to the galaxy
what comets are to our solar system: specimens of relatively
unprocessed, primitive material. (2) For all that, the D/H ratio at
galactic center is lower than in all other places in the galaxy. This
is important evidence confirming that D is not made in stars
and that what D we see is made by the big bang. (3) From models of D
production in quasars, the observed D/H ratio suggests
that the Milky Way could not have harbored a quasar for at least a
billion years and probably not for four billion years. (Lubowich
et al., Nature, 29 June 2000.)
“Recent calculations of the Solar
System’s stability indicate that if the Earth was
removed then Venus and Mercury would become
destabilised in a relatively short time.”
Report: Giant planets may be key to life
(CNN) — The hunt for distant planets similar to Earth should
concentrate on solar systems with planets the size of Jupiter,
according to a new astronomical report.
Such jovian giants could fling celestial objects the size of Mars
toward their central star, transporting the water necessary for
carbon-based life to form on smaller terrestrial worlds, planetary
scientist Jonathan Lunine said last week.
Scientific evidence strongly suggests a similar chain of events
produced our own solar system, the University of Arizona researcher
As the solar system formed, Jupiter’s powerful gravity spurred
asteroids to clump together into increasingly larger objects,
prototypical rocky worlds, he said.
Jupiter then tossed the terrestrial “embyros” into the inner solar
system. Those that hit our planet carried the water that now fills
Earth’s oceans, according to the theory.
The report by Lunine and his colleagues is in the January 30 issue of
the Proceedings of the National Academy of Sciences.
This supports the notion that one rock hitting the right
spot at the right time would have eliminated humans at almost
any time but the last few millenia:
EDINBURGH, Scotland (AP) — Modern Europeans, and maybe populations in
other parts of the world, are descended from no more than a few
hundred Africans who left their homeland as recently as 25,000 years
ago, new research suggests.
Organization, the international collaboration researching the genetic
makeup of the human race, provide the first estimate of how many
people founded Europe.
They are also a blow to the theory that modern humans evolved
simultaneously in Africa, Europe and Asia from multiple early humans.
“I think this certainly rules that out, at least in respect to
Europe,” said study leader Eric Lander, director of the Whitehead
Institute/Massachusetts Institute of Technology Center for Genome
Research. “We’re not sure whether this was just the founding of Europe
or whether, in fact, this small bottleneck represents all the people
Lander’s study involved comparing about 300 chromosomes from people in
Sweden, central Europe and Nigeria. The differences in the genetic
pattern between the European and African chromosomes revealed how long
ago Europeans left Africa and about how many there must have been.
The pattern showed that the Europeans were descended from fewer
ancestors than the Africans — an evolutionary bottleneck, Lander
“It’s hundreds, not thousands,” Lander said.
The Nigerian chromosomes had been well shuffled around, which
indicates a wide gene pool and a long breeding history, while the
European chromosomes had long stretches of unshuffled genetic
material, indicating a much smaller number of chromosome types
entering the mix.
Eddy Rubin, a scientist who was not involved in the study, said he
thinks the findings are accurate.
“The evidence is overwhelming that present-day Europeans come from a
very small group that stayed small for a while, then expanded,” said
Rubin, head of the human genome center at the Lawrence Berkeley
National Laboratory at the University of California, Berkeley.
Lander said the findings had much broader applications.
“We are going to be able to do this throughout much of the rest of the
world. The data will be able to rule it in or out for the other
populations very quickly,” Lander said.
“We’re still in the early days for this, but it is remarkable how much
the human chromosomes can be read as a history book,” he
continued. “We are going to be able to say how populations are related
to each other, when people arrived there and how many people likely
arrived in different places.”
The human race numbers 6 billion people today, but it largely has the
genetic variation of a population of a few tens of thousands, Lander
More evidence of how amazingly closely synchronized human civilization
has been worldwide — climate is the only obvious clock which could
have done this, suggesting just how critical favorable climate has
been to the development of technolife here:
Oldest civilisation in the Americas
Aerial view: Caral’s huge central plaza, surrounded by large pyramids,
seen here as earth mounds An ancient city in what is now Peru was
built at the same time as the great pyramids of Egypt, archaeologists
New evidence indicates the desert site at Caral, on the slopes of the
Andes, was built between 2,600 BC and 2,000 BC.
This date pushes back the emergence of the first complex society in
the New World by nearly 800 years.
And it suggests that the people behind the project were advanced
enough to organise the labour needed to create the architectural
wonder of the day.
Caral is one of 18 sites in central Peru’s Supe Valley, which
stretches eastward from the Pacific coastline, up the slopes of the
All the inland settlements once had architecture on a grand scale,
including the six huge platform mounds seen at Caral.
Because of its size and complexity, archaeologists had thought Caral
was built about 1,500 BC.
But carbon dating of plant samples found at the site add another 1,000
years or so to this figure.
That puts Caral in the same period as the great pyramids of Egypt, and
long before the huge stone structures of Mexico.
“What we’re learning from Caral is going to rewrite the way we think
about the development of early Andean civilisation,” said study leader
Jonathan Haas of the Field Museum in Chicago, US.
The Peruvian-American archaeological team says the pyramids and
irrigation system show an organised society in which masses of people
were paid, or compelled, to work on centralised projects.
This suggests that power and wealth were held by an elite group at a
time when, in most of the Americas, people were still hunting and
gathering in much smaller communities.
“The size of a structure is really an indication of power,” said Haas.
“It means that leaders of the society were able to get their followers
to do lots of work.”
What is surprising to archaeologists is that the city was created by a
society that had yet to invent pottery or cultivate grain.
Its people grew peppers, beans, avocadoes and potatoes – all of which
they roasted, having no pots to boil them in.
They also ate lots of anchovies, which may have been used in dried
form as a kind of currency, as grain was later.
The research is published in the journal Science.
Latest Investigations Of Orion Nebula
Lower Odds Of Planet Formation
In 1993, when the Hubble Space Telescope surveyed the Orion nebula
for the first time, its images provided a substantial boost for the
argument that stars with planetary systems are commonplace in the
galaxy. Now, however, the most recent analyses of one the youngest,
closest and brightest nebulae cast doubt on that conclusion and suggest
that planets may be far rarer than astronomers have thought.
The Orion nebula is the closest example of a stellar nursery. Stellar
nurseries are special regions where the vast majority of new stars in the
galaxy are born. Interstellar clouds of molecular gas form, produce
thousands of new stars and then gradually dissipate. The nebula in
Orion is 1,500 light years from Earth and six light years or 35 trillion
miles across. It forms the second point of light in the hunter?s scabbard
in the Orion constellation. The Trapezium Cluster at the nebula?s
center contains more than 1,500 stars. Four massive young stars
illuminate the nebula, making it possible to observe many objects that
would normally be invisible. The starlight they produce is so intense, in
fact, that it ionizes thin layers of the gas in the region, producing a
rainbow of colors. So it?s not surprising that studies of Orion have
provided astronomers with some of the best information about the
process of star formation.
The first Hubble Space Telescope (HST) images found that up to 90
percent of the young stars in the nebula are surrounded by
“protoplanetary disks”-disks of dust and gas from which planets can
form. Astronomers call such star and disk systems “proplyds.” Based on
the assumption that similar conditions prevail in other stellar nurseries,
the finding strengthened the hypothesis that planet production is a
common side effect of the star formation process.
C. Robert O?Dell, lead scientist on the first HST studies of Orion and
now a research professor at Vanderbilt University, has been studying
the nebula since 1964. In a May 1 presentation at the annual meeting of
the American Physical Society in Washington D.C., O?Dell reports
that the most recent studies of Orion appear to have come up with a
planet stopper. The youngest and brightest stars in the cluster are so
powerful that the ultraviolet radiation they produce should blast away
the dust and gas surrounding newly formed stars before they can form
“According to current estimates, it takes about 10 million years for a
planet to form,” O?Dell says. “The massive, young stars in Orion are
more than 100,000 times as luminous as the sun. Our best estimate is
that these radiation levels can destroy a protoplanetary disk in a few
hundred thousand years. So it appears that most of the disks will be
gone long before planets can form.”
A critical factor in this calculation is the length of time it takes planets
to develop. If planets form considerably faster than scientists currently
think, then the percentage of stars that develop planetary systems could
be substantially higher, O?Dell acknowledges.
Over the last eight years, O?Dell and W. J. Henney at the National
Autonomous University of Mexico at Morelia-working with graduate
students from Rice University and UNAM-have used a combination of
optical and radio telescope data to construct a detailed,
three-dimensional map of the nebula. Using this map, he estimates that
only 10 percent of the proplyds in the nebula are shielded from the
If planetary formation times are correct, and the conditions in the
Orion nebula are typical of stellar nurseries, then only one star in 10 is
likely to form a planetary system, O?Dell says.
Why then does Orion contain more than 300 circumsolar disks? The
answer, according to O?Dell, is quite surprising. One of the stars in
Trapezium turns out to be a binary. By carefully measuring the
properties of this pair of stars, Francesco Palla at the Osservatio
Astrofisico di Arcetri in Italy and Steven Stahler at the University of
California, Berkeley have estimated that it can be no older than 100,000
years. Orion?s massive central stars must be even younger, O?Dell
contends, because they have created an intense radiation environment
that has essentially shut down star formation in the nebula.
“This estimate, combined with the fact that we don?t see any evidence
for depletion of the protoplanetary disks, even those exposed to the
highest radiation levels, suggests that the central stars are even younger,
perhaps only a few tens of thousands of years old,” O?Dell says. The
fact that these stars may not be any older than mankind itself doesn?t sit
well with the astronomer. It goes against the Copernican principle.
Copernicus argued that the Earth wasn?t the center of the universe but,
rather, that the Earth orbits around the Sun. Since then this has been
generalized to the Copernican principle: There is nothing special in
time or space about Earth?s position in the universe.
“It is unlikely that homo sapiens and the Orion nebula should be formed
at just about the same time, but perhaps we are just lucky,” O?Dell says.
By BBC News Online’s Helen Briggs
A mysterious disturbance in the forces at the heart of the Solar
System could have triggered the asteroid that wiped out the dinosaurs.
This intriguing new theory has been put forward by scientists who have
calculated the paths of the planets over the past 100 million years.
A US team believes a change in the dynamics of the Solar System caused
Mercury, the Earth and Mars to veer off course.
This could have pushed a giant asteroid towards our planet, spelling
downfall for most living things, 65 million years ago.
The idea has been floated by a team of astrobiologists at the
University of California, Los Angeles (UCLA), based on simulations of
the historical positions of the major planets.
“Our best calculations show that the dynamical state of the inner
Solar System changed abruptly about 65 million years ago,” said Bruce
Runnegar, director of UCLA’s centre for Astrobiology.
The event modified the average orbit of Mercury, Mars and the Earth in
significant ways, he said, possibly perturbing asteroids in the inner
part of the asteroid belt and throwing one or more of them into
“Thus, the ultimate cause of the K-T impact [and the demise of the
dinosaurs] may have been caused by a chaos-induced change in Solar
System dynamics,” Dr Runnegar told BBC News Online.
The basis of the theory, deduced by team members Ferenc Varadi and
Michael Ghil, is chaos in the Solar System.
Under this scenario, a small shift in the orbit of one or more planets
could destabilise much of the Solar System. To test their theory, the
researchers simulated the orbits of the major planets, working back in
history over tens of millions of years.
To their surprise, computer models pointed to a change in the dynamics
of the inner Solar System at the time of the K-T (Cretaceous-Tertiary)
mass extinction, about 65 million years ago, when many plants and
animals suddenly became extinct.
Dr Runnegar said they were now carrying out further studies to test
“At the moment the link with the dinosaurs is based on a coincidence
in time and a plausible mechanism,” he added.
The research, presented at the Earth System Processes meeting in
Edinburgh, UK, has received a mixed reaction from other experts.
Professor Mark Bailey of the Armagh Observatory, Armagh, said the
asteroid link appeared tenuous, but not impossible.
“[It] relies not least on the assumption that the killer projectile
was an asteroid and not a comet,” he told BBC News Online.
“Nevertheless, the idea that the resonant frequencies of the Solar
System change chaotically on time-scales of tens to hundreds of
millions of years (albeit only slowly and by relatively small amounts)
is an interesting one which adds yet another wrinkle to the story of
our changing Solar System.”
Professor Carlos Frenk, an astrophysicist at the University of Durham,
UK, said the theory appeared plausible.
“If these calculations are correct, they are very revealing of the
unusual past behaviour of the Solar System,” he told BBC News Online.
“The past history of the Solar System was not as quiet as we thought –
this very unusual chaotic behaviour may have happened on our
ET can’t call us if he’s wet
Thursday, 12 July 2001
The search for extra-terrestrial intelligence is
probably a complete waste of time because any
Earth-like planets harbouring life will be too wet to
support the kind of technology needed to “speak”
That’s the essence of a presentation expected to
stimulate “spirited discussion” at an international
conference on life in the universe, to be held at
Sydney’s Macquarie University today.
The global effort to scan the cosmos for radio
signals from intelligent beings on other planets is based
on the belief that a myriad of
earth-like planets exist which might harbour life wanting
to let us know they are “out
Other projects assume extra-terrestrials will communicate
using modulated gravity
waves, laser beams, and neutrino particles.
But Melbourne planetary scientist Dr Nick Hoffman will
tell the Astrobiology Australasia
workshop that even the smartest beings could not develop
the technology to support
such communication systems if they were under water.
In a poster presentation, La Trobe University’s Dr
Hoffman will reveal new calculations
showing the odds of land forming on other Earth-like
planets are “infinitesimally” small.
Instead they would be landless waterworlds.
“‘Waterworlds are the most likely outcome of planet
formation. If you?re in the sea, you
cannot discover fire, so you cannot melt metal to build
machinery, you cannot discover
electricity and you cannot build computers,” Dr Hoffman
told ABC Science Online.
“Sitting here, waiting for someone to ‘phone’ us up is a
waste of time.”
The presence of land on our planet is a direct result of
an extremely rare kind of collision
with asteroids during its formation, Dr Hoffman
says. This collision led to the formation of
our unique type of moon, which is made of materially
formerly part of the primitive Earth’s
The dislodged crust created space on the planet’s surface
into which oceans could
drain. Without that space, the entire surface of the
Earth would be covered with water,
except for the tops of the highest mountains which would
have been eroded by waves.
Dr Hoffman conceded that searching for life in the
universe “gave people something to
look forward to” and so probably did no harm. But he felt
the only real way to discover
other civilisations was to “go there, land on their
waterworld and see them.”
Johns Hopkins University (http://www.jhu.edu)
Ancient Supernova May Have Triggered Eco-Catastrophe
An exploding star may have destroyed part of Earth’s protective ozone
layer 2 million years ago, devastating some forms of ancient marine
life, according to a new theory presented at this week’s meeting of
the American Astronomical Society.
The new theory brings together puzzling clues from several different
fields of research, including paleontology, geology and astronomy.
Narciso Benitez, an associate research scientist in astronomy in the
Krieger School of Arts and Sciences at The Johns Hopkins University,
says the “missing smoking gun” that brought the clues together was the
revelation that a stellar cluster with many large, short-lived stars
prone to producing supernovae had passed near Earth’s solar system
several million years ago.
That discovery, made by co-author and Space Telescope Science
Institute astronomer Jesus Maiz-Apellaniz, led Benitez to check the
scientific record for potential effects of nearby supernovae on the
“Nobody had realized that this cluster of stars that Jesus had
tracked, which is known as the Scorpius-Centaurus OB association,
could have been so close to Earth during the past several million
years,” Benitez says. “And when I did a search, one of the first
things that popped out was a 1999 finding where a team of German
astronomers led by Klaus Knie detected the presence of a highly
unusual isotope of iron in samples of the Earth’s crust drilled from
the deep ocean bottom.”
Knie had proposed that the iron isotope was debris from a recent
supernova explosion that took place close to Earth. But astronomers
had no plausible candidates for such a nearby explosion until
Maiz-Apellaniz’s work with the Scorpius-Centaurus association, which
is also being presented at this week’s meeting of the American
Benitez compared data produced by Maiz-Apellaniz and Knie’s results,
and found “very good agreement, both in the amount of iron deposited
and in its time distribution.”
Benitez consulted with his wife, Matilde Canelles, an immunologist at
the National Institutes of Health who had done her master’s thesis on
microscopic algae, to learn if the paleontological record included an
extinction that had unusual characteristics suggestive of a potential
link to a supernova.
“Such an extinction would have had especially pronounced effects on
the plankton and the marine organisms,” Benitez explains.
Canelles pointed out that evidence existed for a widespread extinction
of plankton and other marine organisms about 2 million years ago, and
noted that scientists are still debating the possible causes of the
“Based on the minimal distance we expected for a supernova in the
Scorpius-Centaurus association at that time, I then did some
calculations to explore the potential effects on Earth,” says Benitez.
He found that cosmic ray emissions from a supernova could have had a
potentially devastating effect on the Earth’s ozone layer, an upper
layer of the atmosphere that absorbs harmful ultraviolet emissions
from the sun and other sources.
“This would have produced a significant reduction in phytoplankton
abundance and biomass, with devastating effects on other marine
populations, such as bivalves,” Benitez says.
Benitez emphasizes that the theory, while provocative, is consistent
with the paleontological evidence, and also with the pattern of
movement of the Scorpius-Centaurus group, which would have been at its
closest to Earth at that time.
He concedes, though, that more evidence will be needed to firmly
establish the theory. In particular, more detailed searches for
supernova-produced isotopes in the geological record would show
whether there was a tight temporal correspondence between the
supernova explosion and the extinction event. Isotope searches could
also offer crucial information about the physical processes involved
in supernova explosions.
“People study supernovae using telescopes and supercomputer
simulations. In the future, some of the most relevant information in
this field may be found in the deep ocean floor,” says Benitez.
While the new theory may further heighten concern about human impacts
on the ozone layer today, Benitez and Maiz-Apellaniz say there’s no
need to worry about another supernova in the Scorpius-Centaurus group
affecting Earth in the near future. The next star due to explode in
the association, Antares, is now located at a distance of almost 500
light-years, which is too far away to have a significant effect on our
This research was funded by an Advanced Camera for Surveys grant from
NASA, the Johns Hopkins Center for Astrophysical Sciences, and a grant
from the Space Telescope Science Institute.
Cosmic catastrophe ‘a certainty’
By Dr David Whitehouse BBC News Online science editor
Sooner or later, a catastrophe from space will wipe out almost all
life on Earth.
According to Dr Arnon Dar, of the Technion Space Research Institute,
Israel, a particular type of exploding star going off anywhere in our
region of the Universe would devastate our planet.
Using the latest statistics and calculations, he argues that a
supermassive star collapsing at the end of its lifetime would form a
black hole and send out a beam of destructive radiation and particles
that would sterilise any planet in its path.
The odds are that any planet in our galaxy would be affected about
once every one hundred million years. “It is a certainty; the
timescales are comparable to mass extinctions seen in Earth’s
geological record,” Dr Dar told BBC News Online.
No hiding place
Supermassive stars, those with a mass substantially greater than our
Sun, are scattered throughout the galaxy. It is thought that when they
collapse at the end of their lives, they eject an intense beam of
radiation, called gamma-rays, into space.
So powerful are these gamma-rays, and the energetic sub-atomic
particles that follow in their wake, that they could have a major
influence on life in our galaxy.
“If such a beam were to strike Earth, the effects would be totally
devastating, unlike anything we could imagine,” Dr Dar said.
On the side of Earth facing the explosion, searing shock waves will
begin to rip through the atmosphere igniting infernos when they reach
Within moments of the arrival of the radiation from deep space, the
atmospheric temperature will begin rising rapidly, wreaking havoc with
global weather systems.
All organic material on the surface of Earth will start to burn.
Survivors will cower in caves and buildings. But the worst is yet to
The initial gamma-ray burst will last a fraction of a second. Almost
immediately afterwards will come the cosmic rays, which will drench
our planet for days. There will be no hiding place.
Cosmic rays are highly energetic particles travelling through space at
almost the speed of light. They will slam into the atmosphere,
depositing vast amounts of energy and creating swarms of destructive
These particles, called muons, will penetrate hundreds of metres into
rocks so that few caves will offer protection and even deep-sea
creatures will be affected by lethal doses of radiation.
The Earth’s ecosystem will be destroyed. “The few who might survive
will wish they had died,” said Dr Dar. “They will struggle, forlornly,
on a wrecked planet.”
Dr Dar points out that many of the great extinctions that regularly
punctuate the Earth’s history are consistent with being caused by a
devastating influx of radiation from space.
“Direct proof that it happened this way is lacking at present,” he
said, “but many people are looking for it.”
There is some good news! Because the gamma-ray bursts from collapsing
supermassive stars are shot across the cosmos in narrow beams,
probably no more than a degree across, most of them will miss the
However, the latest statistics suggest once every one hundred million
years or so, we will be unlucky. Curiously, this is about the rate of
global extinctions on Earth.
At the moment, astronomers do not know which star to watch. Stars,
like the supermassive Eta Carinae, visible in the Southern Hemisphere,
are likely to explode and send out a gamma-ray burst sometime in the
next million years or so. But this particular star is not pointing in
Undoubtedly, there is a star that is, but as yet astronomers have not
found it. But even if they do, will we get any warning?
“Not with our current understanding of science,” said Dr Dar, “but
then science progresses. Perhaps, one day we will be able to tell
which stars are threatening.”
Amid the Universe’s Chaos, a Few Habitable Places
By Robert Roy Britt Senior Science Writer posted: 07:00 am ET 28 May
It took 4.5 billion years for Earth to generate and evolve a life form
that could think, reason, and finally fly off the planet. That’s a
long time, even by cosmic measures. Perhaps too long.
At a time when the only known sentient species has earnestly and
optimistically begun to search for life on other planets, several
scientists within that species have found a host of reasons to guard
the optimism. Throughout the galaxy, hazards to planet formation and
sustained evolution are so serious and varied that life may be
exceedingly rare. Intelligent life, presumably, would be the rarest of
We may, it turns out, be very lucky to be here. However, we may also
turn out to be very alone.
Location, location, location
Guillermo Gonzalez, an Iowa State University expert in stellar
evolution, says there are relatively small bands and patches of the
Milky Way Galaxy that he considers to be habitable regions. There are
places where conditions are just right for the formation of planets
and where things stay calm enough, long enough, to allow the evolution
of anything but the lowest forms of life.
Our Sun happens to be in one of these Goldilocks zones. For now, at
Gonzalez has examined the structure of the galaxy and the amount of
heavy elements distributed through it. The central region of the
galaxy, he says, is far to cramped and chaotic to expect Earth-like
planets to have much chance of developing and remaining stable.
Planetary systems, if they are like ours, are expected to include
outer belts of comets, like our own Oort cloud which extends beyond
Pluto. Near the center of the galaxy, which all astronomers agree is
more densely packed with stars, close encounters between stars would
gravitationally boot more of these comets into the inner reaches of a
solar system, where the planets would be.
Further, because there is a greater concentration of heavy elements —
carbon, iron and other stuff that weighs more than hydrogen and helium
— near the galactic center, Gonzalez said more comets and asteroids
would probably develop.
“Comet showers should be more common,” Gonzalez said at a meeting
titled “Astrophysics of Life” earlier this month at the Space
Telescope Science Institute (STScI).
Conversely, the outer reaches of the galaxy are relatively lean in the
heavier elements, making planet formation difficult according to
present theories. Other researchers have doubted this assertion,
suggesting that regardless of the abundance of heavy elements in a
star’s environment, the quantities can vary greatly within a solar
system, as has been observed in our own.
Galactic Habitable Zone
There are other hazards, however. The pronounced spiral arms of the
Milky Way are regions where star formation is more frequent and
intense. As with the center of the galaxy, gravitational chaos and
heavy radiation in the arms is not conducive to long-running
Between the spiral arms is the only safe place, Gonzalez has been
saying in recent years.
However, while stars orbit the galactic center, they are all on
different courses in relation to the spiral arms and the main, fairly
flat disk of the galaxy. Some stars, during their lifetimes, cross the
spiral arms, and others do not. Other stars travel above, below and
perilously through the main plane.
The Galactic Habitable Zone, which it has come to be called is, then,
actually several shifty places whose bounds are as-yet unclear.
“We don’t know where it is exactly,” Gonzalez said. “We think it’s in
the thin disk of the galaxy. It excludes the center of the galaxy, and
it excludes the outer edge of the galaxy.”
And where are we?
“We’re between spiral arms. We’re going to stay between spiral arms
for a long time.”
Though Gonzalez figures the Sun “undoubtedly” experienced more
dangerous regions of space in the past, he says it isn’t possible to
figure out where we were prior to a few hundred million years
ago. What he does know is that our solar system moves around the
galaxy at a pace and direction that is similar to the nearest spiral
arms, so we will not soon crash through one or be overtaken.
Like Gonzalez, John Bally would love to know where the Sun was
born. Bally, of the University of Colorado, examines the birthplaces
of stars and has learned that the vast majority are generated from
giant clouds of hydrogen that spawn not one, but many stars in a huge
and dense nursery of nearly simultaneous birth.
It’s anything but a pleasant womb.
The clusters are violent, chaotic places whose largest stars —
superhot, massive, short-lived objects — bathe the smaller ones in
heavy doses of ultraviolet radiation that can destroy the seeds of
planets before they ever form.
Here’s what happens:
When stars form, some or perhaps most leave a circle of debris — gas
and dust — that develops into rotating mass called a protoplanetary
disk. From this material, planets, asteroids and comets are thought to
form. At least that’s how it probably happened in our solar
system. Scientists are only beginning to spot and study these dusty
disks around other, relatively nearby stars, and they’ve seen clumps
that hint at planets in the making.
But nearby stars share the relative calm pocket of space — one of
Gonzalez’s habitable zones — that our Sun benefits from. Most star
formation occurs in clusters, and it the bulk of it takes place in the
In these clusters, a few massive stars shine thousands or even
millions of times more brightly than our Sun. Their UV radiation eats
away at the dust disks of other stars, and can strip the planetary
seeds from all nearby stars over the course of a million years or
Meanwhile, other wild interactions are taking place in the dense star
clusters. When a cloud of hydrogen forms stars, it does so because it
contracts and begins to spin. Clumps of greater density form here and
there, Bally explained, and these clumps gain spin and collapse to
“Nearby interactions with multiple stars in a rich cluster can
truncate and even completely eliminate protoplanetary disks,” Bally
All the while, the rotation and gravitational forces can fling stars
hundreds of light-years from their birthplaces. After a few million
years, many of the stars escape the worst radiation environments. And
the large, bully stars pay a price for all their energetic activity —
they typically die within 40 million years.
In an interview, Bally said his research and that of others shows that
around most stars, there is a tight time constraint on when planets
must form before the star’s dust disk is blown away.
“I’m not saying planets can’t form,” he said. “But you have only
100,000 years to a million years.”
Given the roughly 300 billion stars in our galaxy, Bally’s limits
would still allow for plenty of planets out there, but it could also
mean there are far fewer than some researchers have expected. “Either
planetary systems form very fast,” Bally said, “or we will find planet
development to be rare. Something like 5 percent of stars will have
However, if a planet can form quickly — and theorists are not sure
just how long this process takes — then the radiation is irrelevant,
Bally said, and his constraints would be largely lifted.
Our own Sun may have been born in a cluster and later tossed out, but
Bally said it’s not yet possible to figure out if that was the case.
If a planet finds itself around a star that fortuitously plans to hang
out for a long time in a habitable zone of the galaxy, its odds of
supporting life — especially any kind of intelligent life — are
still slim. One only needs consider our own solar system, where
intelligent life exists on just one out of nine planets.
Most planets probably do not end up in habitable zones around their
stars — slim orbital paths where radiation from the star is just
enough to support life but not so much that it evaporates the oceans
away. [The terms “habitable zone” and “Goldilocks zone” were
originally devised to describe these favorable swaths around stars.]
Problem is, planetary habitable zones shift, too.
Kevin Zahnle, an astrobiologist at NASA’s Ames Research Center, said
our Sun has gotten significantly brighter during its roughly 4.6
billion-year life. It emits 30 to 40 percent more radiation than when
Earth was born. Luckily, and possibly because life is present and
moderates the change by evolving and modifying the atmosphere, Earth’s
surface temperature has remained about the same, he said.
Until other possible Earth-like planets are found and studied, no one
can say whether it is commonly possible to preserve such a delicate
Eventually, Earth will be overwhelmed by the change. Within the next 5
billion years or so, the aging Sun will have swollen so much that it
envelops and vaporizes Earth. In just a billion years, the Sun could
be 11 percent brighter than now, turning the planet into an
inhospitable greenhouse. Had it taken another billion years for
humans to evolve, only some real lowlifes would have been around to
deal with the problem.
Only the smart survive
Long before we fry, another asteroid or comet will strike Earth. Every
100,000 years or so, leading experts agree, an impact large enough to
threaten civilization occurs. If other planets are anything like our
own, they too would face this peril of bombardment.
Christopher Chyba of the SETI Institute has theorized that only the
smart can survive. A civilization must evolve to the point that it can
detect and then either detour or destroy threats from space, lest it
be rendered extinct or, at best, plunged back into a Dark Ages
“There is a kind of selection effect for long-lived civilizations,”
Chyba said in comments to a group of reporters during the STScI
conference. “If you want to be long lived, you need to become
technical because you need to be able to observe the impact
environment around you and respond to that environment in some way to
mitigate its effects on your planet.”
Chyba pointed out that it took 700 million years or so for life to
begin on Earth. The planet had to cool down after its initial
formation, and then it weathered a barrage of asteroid impacts. The
largest objects might well have evaporated the oceans, he said,
preventing the origin of life or resetting it if it had already
“Our solar system tells you that life isn’t going to be much younger
than a billion years,” Chyba said. “It’s going to take that long for
the planet to be capable of supporting life at all. It couldn’t be
10,000 years. It couldn’t be a million years.”
Even in an ideal world, there are hazards and limits to life at both
ends. Along the way, it is no picnic. Life is tough, these theorists
all recognize. But it is not impossible. At least one planet has
According to this, Earth should get sterilized only once every
billion years or so, which is hardly a problem at all.
If I recall correctly, there has only been metazoan land-life
on the Earth for about 700 million years. If this report is
correct, perhaps that is all the time you get to evolve
technolife, before the next nearby supernova resets you back
to bare rock:
Threat to Earth from supernova blast falls Wednesday, 4 December 2002
The likelihood of a supernova explosion that would strip off the
Earth’s protective ozone layer for decades and imperil life has been
reduced to a remote threat, according to new calculations by American
The new study, to be published in the March 2003 issue of the
Astrophysical Journal, has calculated that a supernova blast would not
be as damaging, and its range would be lower, than first thought.
To damage our ozone layer, a star would have to go supernova within 25
light years of Earth, which dramatically reduces the chances of an
event to once every 700 million years or so. What’s more, there are no
stars likely to go supernova within a 25 light-year radius, the
Previously, scientists had calculated that a supernova could be 50
light years away and still emit enough gamma rays and other cosmic
radiation to erase most of our ozone layer for decades, exposing the
Earth’s surface to harmful ultraviolet light from the Sun and damaging
cosmic rays from space.
Some scientists have suggested that supernova blasts may have played a
part in past extinction events on Earth.
Dr Neil Gehrels of NASA’s Goddard Space Flight Centre in Maryland,
USA, and colleagues used a detailed computer model of the atmosphere
to gauge how nitrogen oxides – created by gamma rays striking the top
layers – would destroy ozone.
“They found the effect was much less significant than was previously
estimated,” said Dr Chris Tinney, the head of astronomy at the
Anglo-Australian Observatory in Sydney. “The [supernova] would have
to be twice as close to have the same effect.”
The NASA group was looking at one of the ways supernova might wipe out
life on Earth. After a supernova occurred, high energy radiation would
hit our atmosphere, catalysing and breaking down ozone. “It
essentially would de-stabilise our own biosphere, to the point [where]
it would have a significant impact,” Tinney told ABC Science Online.
Since the original calculations were made in the 1970s, astronomers
have learnt a lot more about supernovae, said Tinney. Astronomers have
since debated how much radiation supernovae produce, how the rays
damage the atmosphere and how often stars explode nearby.
The NASA researchers used the energy from Supernova 1987A to make
their new calculations. The supernova was the first ever detected
since modern telescopes were invented, and appeared in the sky in
They found that to thin the ozone layer enough to allow twice as much
ultraviolet light to reach the surface, a star would need to explode
within 25 light years of Earth.
“Twenty-five light years is very close,” said Tinney. “We know all the
stars within 25 light years, and we know that none are massive enough
to go off [in a supernova]. So the number of possible supernovae that
can do this has been reduced to none.”
Only a particular type of star one that is near the end of its life
and above a certain mass can go supernova. “You are in more danger
of being hit by a bus,” said Tinney.
Odds against Earth-like planets
Scientists hope that habitable planets can be found
By Dr David Whitehouse BBC News Online science editor
Earth-like worlds circling stars in orbital zones suitable for life
may be few and far between in the cosmos, according to new research.
In the first comprehensive study of extrasolar planetary systems,
astronomers have shown that in most of them it would not be possible
to keep an Earth-like world in orbit around a star so that it was
neither too hot nor too cold for life.
In general, other planetary systems fall into two types: those with
Jupiter-like worlds circling close to their parent star, and those
with more distant Jupiters in elliptical orbits.
In both systems, maintaining an Earth-like world in a temperate orbit
is difficult, although not in all cases impossible.
“This work shows us just how unusual our own Solar System is when
compared with the other planetary systems,” Dr Kristen Menou of
Princeton University, US, told BBC News Online.
Eighty-five planetary systems were studied, all that were known when
the research was carried out.
Dr Menou said: “They fall into two categories: large planets circling
very close to their sun – the so-called ‘hot Jupiters’, and systems
with Jupiter-like planets in distant non-circular orbits.”
Dr Menou, along with Dr Serge Tabachnik, created computer dynamical
models of the known exoplanetary systems to see if it was possible for
Earth-like worlds to exist for long periods in the so-called habitable
This zone is the region around a star in which a planet would be able
to sustain liquid water, being neither too close to the star for it
all to be vaporised, nor too distant that it all freezes.
In our Solar System, the Earth is in the middle of the habitable zone.
Astronomers believe such a position is essential for life to develop
But it seems difficult for worlds to stay in the habitable zone in the
majority of the extrasolar planetary systems found so far.
“We found that in the systems with the distant Jupiters, these worlds
can disrupt the orbit of any Earth-like world in the habitable zone,”
says Dr Menou.
“Any Earth-like world in the temperate zone would either crash on to
its parent star or be slung out into interstellar space,” he added.
Over half of the planetary systems studied had distant Jupiters making
them unlikely to contain habitable Earth-like worlds.
“We have identified some systems where distant Jupiters would pull
Earth-like worlds into elliptical orbits that keep them inside the
habitable zone. Such worlds would have dramatic and extreme
seasons. We don’t know how that would affect the development of life.”
The new analysis of the systems containing hot Jupiters shows that
Earth-like worlds could remain orbiting in the temperate zone,
seemingly an encouraging finding.
“The good news is that in about a quarter of the systems we studied,
there could be habitable planets present.”
But even in these systems, Earth-like worlds may have been cast
Current models of the evolution of planetary systems have hot-Jupiters
reaching their tight orbits by migrating inwards from more distant
This means that as they slowly travelled sunwards, they would have
scattered any smaller worlds that got in their way, suggesting that
there could be no Earth-like worlds in hot Jupiter systems at all.
“The way we are trying to get out of this pessimistic position,” says
Dr Menou, “is by seeing if Earth-like worlds could form in a planetary
system after the inward migration of Jupiter worlds.”
The research is to be published in a forthcoming edition of the
‘Double whammy’ created the Moon
By Roland Pease
Cosmic collision (William K Hartmann)
Image copyright William K Hartmann
The Moon was probably created in a double-whammy impact, 4.5
billion years ago, which virtually destroyed the Earth as it
The theory, by US astrophysicist Dr Robin Canup, is outlined
in BBC Radio 4’s “An Earth Made for Life” programme.
Like the climax in a firework display, the event was the
culmination of a 100-million-year process in which the Earth
and its neighbouring planets were built through cosmic
collisions between sub-planetary objects. This was the
biggest blow our planet ever experienced.
According to Dr Canup, a proto-planet, something like the
size of Mars, collided at high speed with an Earth that was
nearly fully formed.
The collision was a glancing one. It shattered our Earth,
but pulverised the incoming planet.
Rain of debris
Simulations show the impactor being sprayed out into a
shower of orbiting debris. But within a matter of hours,
much of this had re-grouped to form a new impactor that
smashed into the Earth’s surface a second time.
“At this point, the impacting object was destroyed,” Dr
Canup, of the SouthWest Research Institute, in Boulder,
Colorado, told the BBC.
Most of the impactor rained down onto and became
incorporated into the Earth, the last major component to be
integrated into our planet.
But 10% or so of the mass was spread out into an
incandescent disc around the Earth – a scorching equivalent
of Saturn’s rings.
It was out of this material that the Moon was formed in a
matter of decades.
“At the time it was 15 times closer than the Moon is now,”
says Dr Canup. “So if you had been able to stand on the
surface of the Earth then, you would have seen something
that appeared 15 times the size of what even today is an
impressive full Moon.”
Mike Drake of the Lunar and Planetary Institute calls the
impact “time zero” for the Earth. Anything that had happened
geologically to the Earth before that would have been erased
by the impact.
The planet’s surface was probably melted down to a depth of
1,000 kilometres, cloaking the Earth in a “magma” ocean that
would have radiated like a red-hot furnace.
Tiny grains called “calcium-aluminium rich inclusions” have
been recovered from comets, which are believed to be the
oldest surviving solid pieces of the cloud of dust and gas
that once encircled the forming Sun.
These have been dated to 4.566 billion years ago (give or
take just a couple of million years) and are thought to
represent the kind of stuff that the planets formed from.
The precise date the Moon was formed is still a matter of
debate, but Dr Canup’s research implies it was right at the
end of the planet-building process, which could have taken
up to 100 million years.
Curiously, recent chemical research has shown that the
planet Earth collided with was a twin to the Earth –
scientists have called it “Theia” after the mother of the
Moon in Greek mythology.
Details in the chemistry of the Moon show it to be almost
identical in some key respects to the Earth, although it was
made almost entirely from remnants of the impactor.
Cosmochemist Alex Halliday says that Theia must have been
formed in an orbit almost identical to the Earth’s. Time
zero for Earth, it seems, was the end of time for its twin.
But it wasn’t all destruction. As Robin Canup points out,
the Moon-forming impact gave the Earth its spin on its axis
that now gives us 24-hour days, and stirs up the atmosphere
so that no part of the Earth is too hot or too cold for
And the presence of the Moon gives the Earth a kind of
gravitational counterbalance that stabilises its slightly
inclined axis of rotation – 23 degrees to its orbit – that
gives us the congenial cycle of the seasons over a single
orbit around the Sun.
And the scalding magma ocean, according to Mike Drake, was
(surprisingly) the place where the water of the Earth’s
oceans would have been held – giving our planet one of its
key ingredients for life.
Life’s lucky ‘kick start’
By Dr David Whitehouse
BBC News Online science editor
The Cambrian Explosion – when life suddenly and rapidly flourished
some 550 million years ago – may have an explanation in the reaction
of primitive life to some big event.
Something triggered the explosion of life
The explosion is one of the most significant yet least understood
periods in the history of life on Earth.
New research suggests it may have occurred because of a complex
interaction between components of the biosphere after they had been
disturbed by, for example, the break-up of a super-continent or an
Scientists say the life explosion might just have easily occurred two
billion years earlier – or not at all.
All modern forms of life have their origin in the sudden
diversification of organisms that occurred at the end of the so-called
Scientists have struggled to explain what might have happened in the
previous few hundred million years to trigger such a burst of life.
BIOLOGY’S ‘BIG BANG’
Major animal groups, or phyla, trace lineage to Cambrian Period
Age of trilobites, sea-dwelling arthropods used to date rock layers
Medieval Latin name for Wales, where Cambrian rocks first described
Certainly, it was a period of history that witnessed the assembly and
break-up of two super continents and at least two major glaciation
events. Atmospheric oxygen levels were also on the rise.
But what actually caused the Cambrian Explosion is unknown.
Writing in the journal Geophysical Research Letters, Dr Werner von
Bloh and colleagues, from the Potsdam Institute for Climate Impact
Research, present a new analysis of happened.
They suggest that “feedback” in the biosphere caused it to jump from
one stable state without complex life to one that allowed complicated
life to proliferate.
“We believe that there was a change in the environment – a slow
cooling of the system – that caused positive feedback that allowed the
conditions for complex life,” Dr von Bloh told BBC News Online.
Using a computer model of the ancient Earth, the researchers
considered three components of the biosphere, the zone of life.
These were single-celled life with and without a nucleus, and
multicellular life. Each of these three groups have different
environmental tolerances outside which they cannot thrive.
Simulating the primitive Earth’s biosphere
The computer model showed there were two zones of stability for the
Earth – with or without higher lifeforms – and that 542 million years
ago the planet flipped from one to the other.
What caused the flip is not clear. It might have been a continental
break-up, or even an asteroid impact.
There is some indication that the Moon suffered a sudden increase in
impacts about the same time as the Cambrian Explosion. If so, then the
Earth would have been affected as well.
This latest analysis also provides some support for the Gaia
hypothesis – the idea that the biosphere somehow acts as a
self-sustaining and regulating whole that opposes any changes that
would destroy life on Earth.
Dr von Blow says that after the Cambrian Explosion there has been a
stabilisation of temperature up to the present, and that the biosphere
is not playing a passive role.
He also adds that there is an intriguing implication from his research
which suggests that had the conditions been only slightly different,
the Cambrian Explosion could have occurred two billion years earlier.
An early explosion would have meant that by now the Earth could have
developed far more advanced intelligent creatures than humans.
Alternatively it could still be inhabited by nothing more complex than
Dr von Bloh says that it will be of great interest when we find other
Earth-like worlds circling other stars to see if they have had their
own Cambrian explosions yet.
The timing of such events has implications for the search for
intelligent life in space, he says.
This one is totally new to me! If they are right, it may cut
down the probability of technolife by yet another order of magnitude
per solar system.
About the only thing that is clear so far from detections of
extrasolar planets is that the big gas giants can be found all over
the map, including virtually skimming the surface of the primary, so
location of the gas giants is clearly a critically important real
variability, not just a theoretically possible one.
Meteorites Supplied Earth Life With Phosphorus,
University of Arizona scientists have discovered that meteorites,
particularly iron meteorites, may have been critical to the evolution
of life on Earth.
Their research shows that meteorites easily could have provided more
phosphorus than naturally occurs on Earth — enough phosphorus to give
rise to biomolecules which eventually assembled into living,
Phosphorus is central to life. It forms the backbone of DNA and RNA
because it connects these molecules’ genetic bases into long
chains. It is vital to metabolism because it is linked with life’s
fundamental fuel, adenosine triphosphate (ATP), the energy that powers
growth and movement. And phosphorus is part of living architecture ?
it is in the phospholipids that make up cell walls and in the bones of
“In terms of mass, phosphorus is the fifth most important biologic
element, after carbon, hydrogen, oxygen, and nitrogen,” said Matthew
A. Pasek, a doctoral candidate in UA’s planetary sciences department
and Lunar and Planetary Laboratory.
But where terrestrial life got its phosphorus has been a mystery, he
Phosphorus is much rarer in nature than are hydrogen, oxygen, carbon,
Pasek cites recent studies that show there’s approximately one
phosphorus atom for every 2.8 million hydrogen atoms in the cosmos,
every 49 million hydrogen atoms in the oceans, and every 203 hydrogen
atoms in bacteria. Similarly, there’s a single phosphorus atom for
every 1,400 oxygen atoms in the cosmos, every 25 million oxygen atoms
in the oceans, and 72 oxygen atoms in bacteria. The numbers for carbon
atoms and nitrogen atoms, respectively, per single phosphorus atom are
680 and 230 in the cosmos, 974 and 633 in the oceans, and 116 and 15
“Because phosphorus is much rarer in the environment than in life,
understanding the behavior of phosphorus on the early Earth gives
clues to life’s orgin,” Pasek said.
The most common terrestrial form of the element is a mineral called
apatite. When mixed with water, apatite releases only very small
amounts of phosphate. Scientists have tried heating apatite to high
temperatures, combining it with various strange, super-energetic
compounds, even experimenting with phosphorous compounds unknown on
Earth. This research hasn’t explained where life’s phosphorus comes
from, Pasek noted.
Pasek began working with Dante Lauretta, UA assistant professor of
planetary sciences, on the idea that meteorites are the source of
living Earth’s phosphorus. The work was inspired by Lauretta’s earlier
experiments that showed that phosphorus became concentrated at metal
surfaces that corroded in the early solar system.
“This natural mechanism of phosphorus concentration in the presence of
a known organic catalyst (such as iron-based metal) made me think that
aqueous corrosion of meteoritic minerals could lead to the formation
of important phosphorus-bearing biomolecules,” Lauretta said.
“Meteorites have several different minerals that contain phosphorus,”
Pasek said. “The most important one, which we’ve worked with most
recently, is iron-nickel phosphide, known as schreibersite.”
Schreibersite is a metallic compound that is extremely rare on
Earth. But it is ubiquitous in meteorites, especially iron meteorites,
which are peppered with schreibersite grains or slivered with
pinkish-colored schreibersite veins.
Last April, Pasek, UA undergraduate Virginia Smith, and Lauretta mixed
schriebersite with room-temperature, fresh, de-ionized water. They
then analyzed the liquid mixture using NMR, nuclear magnetic
“We saw a whole slew of different phosphorus compounds being formed,”
Pasek said. “One of the most interesting ones we found was P2-O7 (two
phorphorus atoms with seven oxygen atoms), one of the more
biochemically useful forms of phosphate, similar to what’s found in
Previous experiments have formed P2-07, but at high temperature or
under other extreme conditions, not by simply dissolving a mineral in
room-temperature water, Pasek said.
“This allows us to somewhat constrain where the origins of life may
have occurred,” he said. “If you are going to have phosphate-based
life, it likely would have had to occur near a freshwater region where
a meteorite had recently fallen. We can go so far, maybe, as to say it
was an iron meteorite. Iron meteorites have from about 10 to 100 times
as much schreibersite as do other meteorites.
“I think meteorites were critical for the evolution of life because of
some of the minerals, especially the P2-07 compound, which is used in
ATP, in photosynthesis, in forming new phosphate bonds with organics
(carbon-containing compounds), and in a variety of other biochemical
processes,” Pasek said.
“I think one of the most exciting aspects of this discovery is the
fact that iron meteorites form by the process of planetesimal
differentiation,” Lauretta said. That is, the building-blocks of
planets, called planestesmals, form both a metallic core and a
silicate mantle. Iron meteorites represent the metallic core, and
other types of meteorites, called achondrites, represent the mantle.
“No one ever realized that such a critical stage in planetary
evolution could be coupled to the origin of life,” he added. “This
result constrains where, in our solar system and others, life could
originate. It requires an asteroid belt where planetesimals can grow
to a critical size ? around 500 kilometers in diameter ? and a
mechanism to disrupt these bodies and deliver them to the inner solar
Jupiter drives the delivery of planetesimals to our inner solar
system, Lauretta said, thereby limiting the chances that outer solar
system planets and moons will be supplied with the reactive forms of
phosphorus used by biomolecules essential to terrestrial life.
Solar systems that lack a Jupiter-sized object that can perturb
mineral-rich asteroids inward toward terrestrial planets also have dim
prospects for developing life, Lauretta added.
Pasek is talking about the research today (Aug. 24) at the 228th
American Chemical Society national meeting in Philadelphia. The work
is funded by the NASA program, Astrobiology: Exobiology and
Not a Brick yet, but bears watching:
Deep Sea Sediment Might Have Sparked Evolution
A stellar explosion, like this one, could have changed earth’s climate
German scientists, sifting through dust on the ocean’s floor, have
discovered stardust that may have helped initiate human evolution.
The team of researchers, from the Technical University of Munich,
announced on Wednesday that sediment found at the bottom of the
Pacific Ocean could be from a star explosion 2.8 million years ago
that may have coincided with massive climate change in the world.
About 15,750 feet (4,800 meters) below the surface of the Pacific
Ocean, the scientists found layers of iron-60. The version of iron is
very unusual in that it takes a lot of heat and pressure to make it,
the kind of heat and pressure only a supernova can deliver.
The researchers theorized that a star explosion close to earth was the
only explanation for the sediment’s location on the bottom of the
ocean. They said the layer indicated the star exploded 2.8 million
years ago, showering down iron and cosmic rays.
Working on previous evidence that cosmic ray bombardment could have
opened up the ozone layer, the researchers said the supernova could
have cooked up the earth in such a way as to force climate change.
Anthropologists believe that climate change led to deforestation,
forcing hominids to climb down from the trees and walk erect.
“The African climate shifted towards more arid conditions about 2.8
million years ago,” the researchers, led by Gunther Korschinek,
wrote. “Some of the major events in early hominid evolution appear to
be coeval with African climate changes.”
The discovery comes five years after Korschinek led the team that
first discovered iron-60 sediment in a more shallow area of the
Pacific Ocean. Scientists said at the time that the sediment was
deposited on Earth at the same time as the planet was undergoing
“mini-extinctions,” where species die out at a higher rate than
In a paper published in the New Astronomy Journal, Brian Fields and
John Ellis wrote that the team’s discovery would “constitute the first
direct evidence that a supernova occurred near Earth in the fairly
recent geologic past, with detectable effects on our planet.”
This week’s discovery appears to bolster the claim.
Oxygen May Be Cause Of First Snowball Earth
Denver, Colo. — Increasing amounts of oxygen in the atmosphere could
have triggered the first of three past episodes when the Earth became
a giant snowball, covered from pole to pole by ice and frozen oceans,
according to a Penn State researcher.
Earth & Climate
“We have convincing evidence that at least six of the seven continents
were once glaciated, and we also have evidence that some of these
continents were near the equator when they were covered with ice,”
says Dr. James F. Kasting, professor of geosciences and
meteorology. “Two of these global glaciations occurred at 600 and 750
million years ago, but the earliest occurred at 2.3 billion years
According to Kasting, if it is assumed that the magnetic evidence for
glaciation at the equator is correct, then only two possible
explanations for equatorial glaciation exist.
One is that the Earth’s tilt, which is now at 23.5 degrees from
vertical, was higher than about 54 degrees from vertical. This would
have positioned Earth so that the poles received the most solar energy
and the equator would receive the least, creating a glacier around the
middle but still leaving the poles unfrozen.
The other possibility, which is the one that Kasting leans toward now,
is that the greenhouse gases in the atmosphere fell low enough so that
over millions of years, glaciers gradually encroached from the poles
to 30 degrees from the equator. Then, in about 1,000 years, the
remainder of the Earth rapidly froze due to the great reflectivity of
the already ice-covered areas and their inability to capture heat from
the sun. The entire Earth became a snowball with oceans frozen to more
than a half mile deep.
“For the latest two glaciations, carbon dioxide levels fell low enough
to begin the glaciation process. However, for the earliest glaciation,
the key may have been methane,” Kasting told attendees at the annual
meeting of the Geological Society of America today (Oct. 27) in
Denver. “The earliest known snowball Earth occurred around the time
that oxygen levels in the atmosphere began to rise,” says Kasting, who
is a member of the Penn State Astrobiology Center. “Before then,
methane was a major greenhouse gas in the atmosphere in addition to
carbon dioxide and water vapor.”
As oxygen levels increased, methane levels decreased dramatically and
carbon dioxide levels had not built up enough to compensate, allowing
the Earth to cool. Oxygen levels need only reach a hundredth of a
percent of present-day oxygen levels to convert the methane atmosphere
completely. Once the Earth is snow covered, it takes 5 to 10 million
years for the natural activity of volcanos to increase carbon dioxide
enough to melt the glaciers.
Regardless of the greenhouse gas involved, the pattern of freezing and
defrosting would be the same. Because the sun has been constantly
increasing in brightness, it would take more greenhouse gas in the
past to compensate for the fainter sun. For the glaciations at 600 and
750 million years ago, estimates are that carbon dioxide levels equal
to recent pre-industrial levels or up to three times pre-industrial
levels would have been sufficient for snowball Earth to occur.
Because many continents existed in the warm equatorial areas during
the most recent glaciations, Kasting believes that rapid weathering of
calcium and magnesium silicate rocks, which consumes carbon dioxide,
lowered levels sufficient to cool things.
“It would have taken nearly 300 times present levels of carbon dioxide
to bring the Earth out of its ice cover,” says Kasting. “Then, once
the high reflectivity ice was gone, the carbon dioxide would have
overcompensated and the Earth would become very warm until rapid
weathering would remove carbon dioxide from the atmosphere.”
One reason that many scientists initially rejected the snowball Earth
theory was that biological evidence does not suggest that the various
forms of life on Earth branched out from the latest total
glaciation. A variety of life forms had to survive from before the
glaciation, which is difficult to imagine on an ice-covered
world. Perhaps the ancestors of life today survived in refuges like
hot springs or near undersea thermal vents.
“The biological puzzle of snowball Earth is very interesting,” says
Kasting. “Events suggest that life was more robust than we thought and
that the Earth’s climate was much less stable than we assumed.”
Equatorial Water May Have Provided Means Of Survival
Sudden warming trends melted ice, providing refuge for multi-celled
animals while the rest of the Earth was frozen
The precursor of modern animals may have been able to survive a
Snowball Earth era that occurred some 600 million years ago because of
a belt of open water along the equator, suggests scientists from the
University of Toronto and Texas A&M University. This was a time
considered critical in the evolutionary development of multi-celled
animals and therefore the most important interval for biological
evolution in general.
In a paper to be published in the May 25 edition of Nature, University
of Toronto physics professor Richard Peltier and Texas A&M
oceanographers William Hyde, Thomas Crowley and Steven Baum note that
the late Proterozoic era (600-800 million years ago) was the most
important period of evolution for multi-cellular creatures. However,
this period was also a time in Earth’s history that has come to be
referred to as the Snowball Earth. At that time, the planet was
thought to be completely ice-covered. Geological and paleomagnetic
evidence indicates that for alternating periods, the Earth was
completely covered by ice sheets over the continents and sea ice over
the oceans, followed by sudden warming trends that melted the ice.
“If the suface of the planet was covered by ice, the question arises
as to how early life managed to survive under such environmental
stress,” says Peltier. To find an answer, the scientists employed
several different models of the climate systems and ran detailed
computer simulations of the climate thought to have been
characteristic of that time. To simulate the Snowball Earth, they
reduced the amount of sunlight reaching the Earth — to account for
the fact that the sun was about six per cent less luminous than it is
now — and varied the concentration of atmospheric carbon dioxide
within the range expected for that time.
In most of the simulations, their analysis revealed the presence of a
belt of open water near the equator when the general circulation of
the ocean was taken into account. “It is this open water that may have
provided a refuge for multi-celled animals when the rest of the Earth
was covered by ice and snow,” Peltier explains.
The findings of this research are critical to understanding how early
life evolved, he states. “This could help clarify how multi-celled
animals managed not only stay alive, but to thrive given the Earth’s
harsh conditions. The extreme climates may even have exerted pressure
on these animals to evolve and adapt, possibly leading to the rapid
development of new forms of animals and their movement into new,
unpopulated habitats when the Earth exited the snowball state. It was
during the warm Cambrian era — immediately following the late
Proterozoic — in which life proliferated.”
The late Proterozoic period was also a time when the supercontinents
Rodinia and Pannotia formed and subsequently rifted and
disassembled. Located over the south rotational pole in the position
of present-day Antarctica, these supercontinents were made up of the
current land masses of Africa, South America, Antarctica, Australia,
Greenland, Laurentia and parts of Asia. According to Peltier, the
entry of the Earth into the snowball state required not only the weak
sun and atmospheric carbon dioxide levels not significantly higher
than present-day, but also this high degree of polar continentality.
Scientists Find Evolution Of Life Helped Keep Earth Habitable
LIVERMORE, Calif. — A trio of scientists including a researcher from
the Lawrence Livermore National Laboratory has found that humans may
owe the relatively mild climate in which their ancestors evolved to
tiny marine organisms with shells and skeletons made out of calcium
In a paper titled “Carbonate Deposition, Climate Stability and
Neoproterozoic Ice Ages” in the Oct. 31 edition of Science, UC
Riverside researchers Andy Ridgwell and Martin Kennedy along with LLNL
climate scientist Ken Caldeira, discovered that the increased
stability in modern climate may be due in part to the evolution of
marine plankton living in the open ocean with shells and skeletal
material made out of calcium carbonate. They conclude that these
marine organisms helped prevent the ice ages of the past few hundred
thousand years from turning into a severe global deep freeze.
“The most recent ice ages were mild enough to allow and possibly even
promote the evolution of modern humans,” Caldeira said. “Without these
tiny marine organisms, the ice sheets may have grown to cover the
earth, like in the snowball glaciations of the ancient past, and our
ancestors might not have survived.”
The researchers used a computer model describing the ocean, atmosphere
and land surface to look at how atmospheric carbon dioxide would
change as a result of glacier growth. They found that, in the distant
past, as glaciers started to grow, the oceans would suck the
greenhouse gas — carbon dioxide out of the atmosphere — making the
Earth colder, promoting an even deeper ice age. When marine plankton
with carbonate shells and skeletons are added to the model, ocean
chemistry is buffered and glacial growth does not cause the ocean to
absorb large amounts of carbon dioxide from the atmosphere.
But in Precambrian times (which lasted up until 544 million years
ago), marine organisms in the open ocean did not produce carbonate
skeletons — and ancient rocks from the end of the Precambrian
geological age indicate that huge glaciers deposited layers of crushed
rock debris thousands of meters thick near the equator. If the land
was frozen near the equator, then most of the surface of the planet
was likely covered in ice, making Earth look like a giant snowball,
the researchers said.
Around 200 million years ago, calcium carbonate organisms became
critical to helping prevent the earth from freezing over. When the
organisms die, their carbonate shells and skeletons settle to the
ocean floor, where some dissolve and some are buried in
sediments. These deposits help regulate the chemistry of the ocean and
the amount of carbon dioxide in the atmosphere. However, in a related
study published in Nature on Sept. 25, 2003, Caldeira and LLNL
physicist Michael Wickett found that unrestrained release of
fossil-fuel carbon dioxide to the atmosphere could threaten extinction
for these climate-stabilizing marine organisms.
Datum: Despite long-term 30% increase in solar brightness, the
biosphere seems exquisitely sensistive to fluctuations in the
Major Climate Change Occurred 5,200 Years Ago: Evidence Suggests That
History Could Repeat Itself
December 16, 2004
Glaciologist Lonnie Thompson worries that he may have found clues that
show history repeating itself, and if he is right, the result could
have important implications to modern society.
Thompson has spent his career trekking to the far corners of the world
to find remote ice fields and then bring back cores drilled from their
centers. Within those cores are the records of ancient climate from
across the globe.
From the mountains of data drawn by analyzing countless ice cores, and
a meticulous review of sometimes obscure historic records, Thompson
and his research team at Ohio State University are convinced that the
global climate has changed dramatically.
But more importantly, they believe it has happened at least once
before, and the results were nearly catastrophic to emerging cultures
at the time. He outlined his interpretations and fears today at the
annual meeting of the American Geophysical Union in San Francisco.
A professor of geological sciences at Ohio State and a researcher with
the Byrd Polar Research Center, Thompson points to markers in numerous
records suggesting that the climate was altered suddenly some 5,200
years ago with severe impacts.
He points to perfectly preserved plants he discovered that recently
emerged from the Quelccaya ice cap in the Peruvian Andes as that
glacier retreats. This monstrous glacier, some 551 feet (168 meters)
deep, has shown an exponentially increasing rate of retreat since his
first observations in 1963.
The plants were carbon-dated to determine their age and tests
indicated they had been buried by the ice for perhaps 5,200
years. That suggests that somehow, the climate had shifted suddenly
and severely to capture the plants and preserve them until now.
In 1991, hikers found the preserved body of a man trapped in an Alpine
glacier and freed as it retreated. Later tests showed that the human ”
dubbed Oetzi ” became trapped and died around 5,200 years ago.
Thompson points to a study of tree rings from Ireland and England that
span a period of 7,000 years. The point in that record when the tree
rings were narrowest ” suggesting the driest period experienced by the
trees ” was approximately 5,200 years ago.
He points to ice core records showing the ratio of two oxygen isotopes
retrieved from the ice fields atop Africa”s Mount Kilimanjaro. A proxy
for atmospheric temperature at the time snow fell, the records are at
their lowest 5,200 years before now.
He lists the shift by the Sahara Desert from a habitable region to a
barren desert; major changes in plant pollen uncovered from lakebed
cores in South America, and the record lowest levels of methane
retrieved from ice cores from Greenland and Antarctica and all
occurred at the same time ” 5,200 years ago.
“Something happened back at this time and it was monumental,” Thompson
said. “But it didn”t seem monumental to humans then because there were
only approximately 250 million people occupying the planet, compared
to the 6.4 billion we now have.
“The evidence clearly points back to this point in history and to some
event that occurred. It also points to similar changes occurring in
today”s climate as well,” he said.
“To me, these are things we really need to be concerned about.”
The impact of a climate change of that magnitude on a modern world
would be tremendous, he said. Seventy percent of the population lives
in the world”s tropics and major climate changes would directly impact
most of them.
Thompson believes that the 5,200-year old event may have been caused
by a dramatic fluctuation in solar energy reaching the
earth. Scientists know that a historic global cooling called the
Little Ice Age, from 1450 to 1850 A.D., coincided with two periods of
decreased solar activity.
Evidence shows that around 5,200 years ago, solar output first dropped
precipitously and then surged over a short period. It is this huge
solar energy oscillation that Thompson believes may have triggered the
climate change he sees in all those records.
“The climate system is remarkably sensitive to natural variability,”
he said. “It”s likely that it is equally sensitive to effects brought
on by human activity, changes like increased greenhouse gases, altered
land-use policies and fossil-fuel dependence.
“Any prudent person would agree that we don”t yet understand the
complexities with the climate system and, since we don’t, we should be
extremely cautious in how much we “tweak” the system,” he said.
“The evidence is clear that a major climate change is underway.”
Comets, Meteors & Myth
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
13 November 2001
“…and the seven judges of hell … raised their torches, lighting
the land with their livid flame. A stupor of despair went up to heaven
when the god of the storm turned daylight into darkness, when he
smashed the land like a cup.”
— An account of the Deluge from the Epic of Gilgamesh, circa 2200
If you are fortunate enough to see the storm of shooting stars
predicted for the Nov. 18 peak of the Leonid meteor shower, you’ll be
watching a similar but considerably less powerful version of events
which some scientists say brought down the world’s first
The root of both: debris from a disintegrating comet.
Biblical stories, apocalyptic visions, ancient art and scientific data
all seem to intersect at around 2350 B.C., when one or more
catastrophic events wiped out several advanced societies in Europe,
Asia and Africa.
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A 1994 image of Comet Borrelly on one of its swings around the Sun.
Norwegian astrophotographer Arne Danielsen captured this spectacular
Leonid fireball on November 18, 1999.
Related SPACE.com STORIES
Leonids 2002 Special Report
The Origin of Sex: Cosmic Solution to Ancient Mystery
Reinventing Darwin Again: How Asteroids Impacted Human Evolution
Engineering ET: The Path to Alternate Life Forms
Survival of the Elitist: Bioterrorism May Spur Space Colonies
What do you think of this story?
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Increasingly, some scientists suspect comets and their associated
meteor storms were the cause. History and culture provide clues: Icons
and myths surrounding the alleged cataclysms persist in cults and
religions today and even fuel terrorism.
And a newly found 2-mile-wide crater in Iraq, spotted serendipitously
in a perusal of satellite images, could provide a smoking gun. The
crater’s discovery, which was announced in a recent issue of the
journal Meteoritics & Planetary Science, is a preliminary
finding. Scientists stress that a ground expedition is needed to
determine if the landform was actually carved out by an impact.
Yet the crater has already added another chapter to an intriguing
overall story that is, at best, loosely bound. Many of the pages are
washed away or buried. But several plot lines converge in conspicuous
Too many coincidences
Archeological findings show that in the space of a few centuries, many
of the first sophisticated civilizations disappeared. The Old Kingdom
in Egypt fell into ruin. The Akkadian culture of Iraq, thought to be
the world’s first empire, collapsed. The settlements of ancient
Israel, gone. Mesopotamia, Earth’s original breadbasket, dust.
Around the same time — a period called the Early Bronze Age —
apocalyptic writings appeared, fueling religious beliefs that persist
The Epic of Gilgamesh describes the fire, brimstone and flood of
possibly mythical events. Omens predicting the Akkadian collapse
preserve a record that “many stars were falling from the sky.” The
“Curse of Akkad,” dated to about 2200 B.C., speaks of “flaming
potsherds raining from the sky.”
Roughly 2000 years later, the Jewish astronomer Rabbi bar Nachmani
created what could be considered the first impact theory: That Noah’s
Flood was triggered by two “stars” that fell from the sky. “When God
decided to bring about the Flood, He took two stars from Khima, threw
them on Earth, and brought about the Flood.”
Another thread was woven into the tale when, in 1650, the Irish
Archbishop James Ussher mapped out the chronology of the Bible — a
feat that included stringing together all the “begats” to count
generations — and put Noah’s great flood at 2349 B.C.
A number of scientists don’t think so.
Mounting hard evidence collected from tree rings, soil layers and even
dust that long ago settled to the ocean floor indicates there were
widespread environmental nightmares in the Near East during the Early
Bronze Age: Abrupt cooling of the climate, sudden floods and surges
from the seas, huge earthquakes.
Comet as a culprit
In recent years, the fall of ancient civilizations has come to be
viewed not as a failure of social engineering or political might but
rather the product of climate change and, possibly, heavenly
happenstance. As this new thinking dawned, volcanoes and earthquakes
were blamed at first. More recently, a 300-year drought has been the
But now more than ever, it appears a comet could be the culprit. One
or more devastating impacts could have rocked the planet, chilled the
air, and created unthinkable tsunamis — ocean waves hundreds of feet
high. Showers of debris wafting through space — concentrated versions
of the dust trails that create the Leonids — would have blocked the
Sun and delivered horrific rains of fire to Earth for years.
So far, the comet theory lacks firm evidence. Like a crater.
Now, though, there is this depression in Iraq. It was found
accidentally by Sharad Master, a geologist at the University of
Witwatersrand in South Africa, while studying satellite images. Master
says the crater bears the signature shape and look of an impact caused
by a space rock.
The finding has not been developed into a full-fledged scientific
paper, however, nor has it undergone peer review. Scientist in several
fields were excited by the possibility, but they expressed caution
about interpreting the preliminary analysis and said a full scientific
expedition to the site needs to be mounted to determine if the
landforms do in fact represent an impact crater.
Researchers would look for shards of melted sand and telltale quartz
that had been shocked into existence. If it were a comet, the impact
would have occurred on what was once a shallow sea, triggering massive
flooding following the fire generated by the object’s partial
vaporization as it screamed through the atmosphere. The comet would
have plunged through the water and dug into the earth below.
If it proves to be an impact crater, there is a good chance it was dug
from the planet less than 6,000 years ago, Master said, because
shifting sediment in the region would have buried anything older.
Arriving at an exact date will be difficult, researchers said.
“It’s an exciting crater if it really is of impact origin,” said Bill
Napier, an astronomer at the Armagh Observatory.
Napier said an impact that could carve a hole this large would have
packed the energy of several dozen nuclear bombs. The local effect:
“But the cultural effect would be far greater,” Napier said in an
e-mail interview. “The event would surely be incorporated into the
world view of people in the Near East at that time and be handed down
through the generations in the form of celestial myths.”
Napier and others have also suggested that the swastika, a symbol with
roots in Asia stretching back to at least 1400 B.C., could be an
artist’s rendering of a comet, with jets spewing material outward as
the head of the comet points earthward.
But could a single impact of this size take down civilizations on
three continents? No way, most experts say.
Napier thinks multiple impacts, and possibly a rain of other smaller
meteors and dust, would have been required. He and his colleagues have
been arguing since 1982 that such events are possible. And, he says,
it might have happened right around the time the first urban
civilizations were crumbling.
Napier thinks a comet called Encke, discovered in 1786, is the remnant
of a larger comet that broke apart 5,000 years ago. Large chunks and
vast clouds of smaller debris were cast into space. Napier said it’s
possible that Earth ran through that material during the Early Bronze
The night sky would have been lit up for years by a fireworks-like
display of comet fragments and dust vaporizing upon impact with
Earth’s atmosphere. The Sun would have struggled to shine through the
debris. Napier has tied the possible event to a cooling of the
climate, measured in tree rings, that ran from 2354-2345 B.C.
Though no other craters have been found in the region and precisely
dated to this time, there is other evidence to suggest the scenario is
plausible. Two large impact craters in Argentina are believed to have
been created sometime in the past 5,000 years.
Benny Peiser, a social anthropologist at Liverpool John Moores
University in England, said roughly a dozen craters are known to have
been carved out during the past 10,000 years. Dating them precisely is
nearly impossible with current technology. And, Peiser said, whether
any of the impact craters thought to have been made in the past 10,000
years can be tied back to a single comet is still unknown.
But he did not discount Napier’s scenario.
“There is no scientific reason to doubt that the break-up of a giant
comet might result in a shower of cosmic debris,” Peiser said. He also
points out that because Earth is covered mostly by deep seas, each
visible crater represents more ominous statistical possibilities.
“For every crater discovered on land, we should expect two oceanic
impacts with even worse consequences,” he said.
Tsunamis generated in deep water can rise even taller when they reach
Next Page: Terrorism of today rooted in ancient impacts
Peiser studies known craters for clues to the past. But he also
examines religions and cults, old and new, for signs of what might
have happened way back then.
“I would not be surprised if the notorious rituals of human sacrifice
were a direct consequence of attempts to overcome this trauma,” he
says of the South American impact craters. “Interestingly, the same
deadly cults were also established in the Near East during the Bronze
The impact of comets on myth and religion has reverberated through the
ages, in Peiser’s view.
“One has to take into consideration apocalyptic religions [of today]
to understand the far-reaching consequences of historical impacts,” he
says. “After all, the apocalyptic fear of the end of the world is
still very prevalent today and can often lead to fanaticism and
An obsession with the end of the world provides the legs on which
modern-day terrorism stands, Peiser argues. Leaders of fundamentalist
terror groups drum into the minds of their followers looming
cataclysms inspired by ancient writings. Phrases run along these
lines: a rolling up of the sun, darkening of the stars, movement of
the mountains, splitting of the sky.
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>>Go to Science Tuesday archive page
A 1994 image of Comet Borrelly on one of its swings around the Sun.
Norwegian astrophotographer Arne Danielsen captured this spectacular
Leonid fireball on November 18, 1999.
Related SPACE.com STORIES
Leonids 2002 Special Report
The Origin of Sex: Cosmic Solution to Ancient Mystery
Reinventing Darwin Again: How Asteroids Impacted Human Evolution
Engineering ET: The Path to Alternate Life Forms
Survival of the Elitist: Bioterrorism May Spur Space Colonies
What do you think of this story?
>>Uplink your views
It is in the context of such apocalyptic religions that a large
meteorite, enshrined in the Kaba in Mecca, became the most feared and
venerated object of the Islamic faith, Peiser said.
By using such language, radical fundamentalist leaders instill
“absolute commitment and fanaticism into their followers,” Peiser
said. “Once you believe that the end is imminent and that your direct
action will hasten the coming of end-times, every atrocity is
No smoking gun yet
Despite the excitement of the newfound hole in the ground in Iraq, it
is still far from clear why so many civilizations collapsed in such a
relatively short historical time frame. Few scientists, even those who
find evidence to support the idea, are ready to categorically blame a
French soil scientist Marie-Agnes Courty, who in 1997 found material
that could only have come from a meteorite and dated it to the Early
Bronze Age, urged caution on drawing any conclusions until a smoking
gun has been positively identified.
“Certain scientists and the popular press do prefer the idea of
linking natural catastrophes and societal collapse,” Courty said.
Multiple cosmic impacts are an attractive culprit though, because of
the many effects they can have, including some found in real climate
and geologic data. The initial impact, if it is on land, vaporizes
life for miles around. Earthquakes devastate an even wider area. A
cloud of debris can block out the Sun and alter the climate. The
extent and duration of the climate effects is not known for sure,
because scientists have never witnessed such an event.
It might not have taken much. Ancient civilizations, which depended on
farming and reliable rainfall, were precarious.
Mike Baillie, a professor of palaeoecology at Queens University in
Belfast, figures it would have taken just a few bad years to destroy
such a society.
Even a single comet impact large enough to have created the Iraqi
crater, “would have caused a mini nuclear winter with failed harvests
and famine, bringing down any agriculture based populations which can
survive only as long as their stored food reserves,” Baillie said. “So
any environmental downturn lasting longer than about three years tends
to bring down civilizations.”
Other scientists doubt that a single impact would have altered the
climate for so long.
Lessons for tomorrow
Either way, there is a giant scar on the planet, near the cradle of
civilization, that could soon begin to provide some solid answers,
assuming geologists can get permission to enter Iraq and conduct a
“If the crater dated from the 3rd Millennium B.C., it would be almost
impossible not to connect it directly with the demise of the Early
Bronze Age civilizations in the Near East,” said Peiser.
Perhaps before long all the cometary traditions, myths and scientific
fact will be seen to converge at the Iraqi hole in the ground for good
purpose. Understanding what happened, and how frequent and deadly such
impacts might be, is an important tool for researchers like Peiser who
aim to estimate future risk and help modern society avoid the fate of
“Paradoxically, the Hebrew Bible and other Near Eastern documents have
kept alive the memory of ancient catastrophes whose scientific
analysis and understanding might now be vital for the protection of
our own civilizations from future impacts,” Peiser said.
Experts weigh super-volcano risks
By Paul Rincon
BBC News science reporter
The drama imagines what a super-eruption at Yellowstone would be like
Geologists have called for a taskforce to be set up to consider emergency management in the event of a massive volcanic eruption, or super-eruption.
The recommendation comes in a report timed to coincide with a BBC TV drama that depicts a fictional super-eruption at Yellowstone Park in Wyoming, US.
Experts say such an event would have a colossal impact on a global scale.
A super-eruption is also five to 10 times more likely to happen than an asteroid impact, the report claims.
We don’t want to be sensationalist about this, but it’s going to happen
Prof Stephen Self, Open University
The authors want to highlight the issue, which they feel is being ignored by governments. They emphasise that while catastrophic eruptions of this kind are rare in terms of a human lifetime, they are surprisingly common on a geological scale.
The effects, say the authors, “could be sufficiently severe to threaten the fabric of civilisation” – putting events such as the Asian tsunami into the shade.
The fallout from a super-eruption could cause a “volcanic winter”, devastating global agriculture and causing mass starvation.
It would have a similar effect to a 1.5km-diameter space rock striking Earth, they claim.
But while impacts of this type are estimated to occur once every 400-500,000 years, the frequency of equivalent super-eruptions is about once every 100,000 years.
“These are minimum estimates. Super-eruptions could be even more frequent; we just don’t know,” said Professor Stephen Self, a geologist at the Open University in Milton Keynes and a member of the working group that produced the report.
Mount Pinatubo, USGS
The Mount Pinatubo eruption was the biggest recorded in photos
“We still have a lot of unassessed regions of the world. The US is the place where we see the largest number of super-eruptions. But that may be because more work has been done there.”
One past super-eruption struck at Toba in Sumatra 74,000 years ago and is thought by some to have driven the human race to the edge of extinction. Signs from DNA suggest human numbers could have dropped to about 10,000, probably as a result of the effects of climate change.
The TV drama, called Supervolcano, sticks closely to scientific understanding of these events.
The plot revolves around a series of violent eruptions at Yellowstone in Wyoming that send thousands of cubic metres of rock, gas and ash spiralling up in cloud that rains down over three-quarters of the United States.
Highways become blocked with cars as millions flee the unfolding disaster, and as the chain of eruptions unzips Yellowstone’s volcanic crater, hundreds of thousands are killed as the ash swamps whole towns and cities.
Yellowstone geyser, USGS
Yellowstone is the largest volcanic system in North America
America’s food-producing regions are devastated, communications are knocked out and planes are forced out of the sky.
Sulphuric acid droplets form in the atmosphere, blocking out sunlight, and causing global temperatures to plummet.
Professor Stephen Sparks, of Bristol University, an author on the new report, said civil contingency plans would need to be similar to those for a nuclear war.
“You would need contingencies for food and shelter. But you would need to put a serious amount of resources into any effort to cope with an event on this scale, so it poses a dilemma,” he said.
The volcanic winter resulting from a super-eruption could last several years or decades, depending on the scale of an eruption, and according to recent computer models, could cause cooling on a global scale of 5-10C.
Ailsa Orr, producer of Supervolcano, said that when the programme team presented the scenario to the US Federal Emergency Management Agency (Fema), the agency admitted it had given little thought to such an event happening on American soil.
“We don’t want to be sensationalist about this, but it’s going to happen. We just can’t say exactly when,” said Professor Self.
“But we have just had a natural disaster affecting hundreds of thousands of people. Now is the time to be thinking about this.”
Yellowstone is the largest volcanic system in North America. The area’s cauldrons of bubbling mud and roaring geysers attract nearly three million visitors each year.
It was an obvious choice for the programme makers as the site of their super-eruption because of its location on a highly populated continent and because it has already had three of these events, which have occurred roughly 600,000 years apart from each other.
The crater from the last super-eruption, 640,000 years ago, is large enough to fit Tokyo – the world’s biggest city – inside it.
The report, released by The Geological Society in the UK, identifies at least 31 sites where super-eruptions have occurred in the past. They include Lake Taupo in New Zealand and the Phlegrean Fields near Naples, Italy.
Sea life ‘killed by exploding star’
Alok Jha, science correspondent
Monday April 11, 2005
A huge blast of radiation from an exploding star might have been
behind one of the Earth’s worst mass extinctions, some 450m years ago.
In the latest issue of the Astrophysical Journal Letters, scientists
argue that a gamma ray burst, the most powerful explosion that occurs
in the universe, was responsible for the Ordovican mass extinction in
which 60% of all marine invertebrates died.
Gamma ray bursts are thought to be caused either when two neutron
stars collide or when giant stars collapse into black holes at the end
of their lives.
For around 10 seconds, intense pulses of energy are fired off, which
can be detected right across the universe. All the bursts recorded by
astronomers so far have come from distant galaxies and are therefore
harmless to the Earth.
But if a burst occurred in our own galaxy, the effect would be
Dr Adrian Melott, of the University of Kansas and an author of the
latest paper, said: “A gamma ray burst originating within 6,000 light
years from Earth would have a devastating effect on life.
“We don’t know exactly when one came, but we’re rather sure it did
come – and left its mark.”
Such a burst would strip the Earth of its protective ozone layer,
allowing deadly ultraviolet radiation to pour down from the sun.
Computer models showed that up to half the ozone layer could be
destroyed within weeks. Five years later, at least 10% would still be
Using computer models, the researchers calculated that plankton and
other life in the first few feet of the oceans would have been
The knock-on effect would have been huge: plankton are at the bottom
of the marine food chain providing for animals which are then preyed
upon by larger species.
Previously, scientists thought that an ice age caused the Ordovican
extinction. A gamma ray burst would have had a similar effect, causing
a fast die-off early on and triggering a significant drop in surface
Astronomers are planning to launch a robot spacecraft to study the
mysterious gamma ray bursts further.
Because the bursts happen suddenly and are so short, scientists have
been lucky to detect one a month with instruments on Earth.
Next month, Nasa will launch the £138m Swift probe, which will sweep
up to one sixth of the sky at a time, looking for sudden bursts. If
all goes well, the probe could catch two three explosions a week.
Telescope views galaxy collision
Image: Gemini Observatory
New stars and planets may be forming within the old galaxies (Image:
Two galaxies collide in the constellation of Pisces, some 100 million
light-years away from Earth.
Astronomers say it gives an insight into what may happen to our own
region of space some 5 billion years from now. The Milky Way is
expected to merge with the neighbouring Andromeda Galaxy, and
swallowing up our Solar System.
The image was captured last month by an instrument on the Gemini North
Telescope at Mauna Kea, Hawaii.
Professor Ian Robson, director of the UK Astronomy Technology Centre,
which built the instrument, said that when he first saw the image, it
sent shivers down his spine.
“Our saving grace is that we have about 5 billion years left before we
get swallowed up by Andromeda,” he said.
“Nevertheless, it’s amazing to see so far in advance how planet Earth
and our own galaxy will ultimately end. Glad to say I won’t be around
when the fireball happens.”
The combined galaxies, known as NGC 520, have lost their shape as a
result of the collision. Astronomers believe new stars are forming in
the faint red glowing areas seen above and beneath the middle of the
It is one of many snapshots of distant galaxies and star forming
regions taken by the Gemini Multi-Object Spectrograph (GMOS) since it
was installed in 2001.
Brick: Hypervariable climate
One brick is the hypervariability of the modern
climate, which is a direct function of the
extraordinarily peculiar modern arrangement of
Our planet is mostly water, and this is also
a precondition to the rise of life. If surface
water on the planet were limited to lakes, the
climate would be too unstable for technolife
to evolve. Every little cooling episode would
freeze all the surface water on the planet
solid to the bottom of the lakes, wiping out
If you take a mostly-water planet with
plate tectonics, most of the time what
you get is one supercontinent surrounded
by a huge world ocean.
The world ocean acts as a huge climate-change
damper, and climate on the supercontinent is the
same for tens of millions of years at a stretch:
“This is DINO radio. Weather forecast is
for hot and humid, rainy with daily sunbreaks,
through the end of the geological era, with
massive volcanic outflows and outgassing heading
into the next era. Over to you for sports, Tom.”
When the supercontinent -does- break up, it
usually still consists just of a few continents
spotted around the equator and one pole, leaving
the world ocean intact as a climatic damper
But WE live in a totally strange age when the
supercontinent essentially elongated into a
vertical barrier blocking the world ocean
effectively pole-to-pole — and THEN split
neatly in half lengthwise, producing the
Atlantic ocean, which is essentially a
tuned cavity running north-south pole to
pole, cut off from the rest of the world
ocean for most practical purpose.
“HOW WEIRD IS THAT?!!??” 
Nor is this oddity merely an interesting bit
of geographic ornamentation for the continental
On the contrary, from a climate-change point of
view, it is the overwhelmingly dominant
characteristic of the era!
The tuned-pipe ringing of the Atlantic ocean has
the entire planet going from hot to cold and back
again in tens of thousands of years, when it would
usually take tens of millions of years — which is
to say, a thousand times faster than usual.
For the last couple of million years, during which
humans evolved, the climate organ has been hitting
a crescendo of hypervariability:
HUMANS EVOLVED AT THE PEAK OF THE MOST HYPERVARIABLE
CLIMATE OSCILLATION PATTERN IN THE HISTORY OF THE
Is it coincidence that a “specializing generalist” 
species like Homo Sapiens sapiens happened to evolve
during such a peak in climatic variability?
I THINK NOT!
The “jack of all trades is a master of none”: In
a time of stable climates, the specializing generalist
is liable to be driven to extinction by
specializing specialists which are better at whatever
matters at the time.
The ability to adapt doesn’t cut any
evolutionary ice during eras when the
environment doesn’t exercise that ability.
During those sorts of times — which is
to say, during geologically NORMAL times
— the ability to adapt is just evolutionary
baggage, like eyes on cave fish living without
light, and like the eyes on those fish, is
going to atrophy in a geological instant:
A thirty-watt brain is a HUGE metabolic
liability in an era when there’s no use
Only in an era when change is too rapid for the
specializing specialists to keep up via
evolutionary adaptation is the specializing
generalist able to compete.
-> Human civilization was able to blossom during the
-> last 10,000 years because when the ice receded,
-> human cultural adaptation allowed them to
-> recolonize the planet faster than species which
-> depended upon evolution to adapt to the newly
-> warm conditions.
In short, humans only discovered the Americas
in the last 10,000 years, but the relationship
goes back for millions of years, because it was
in fact the Americas which CREATED humans.
# A necessary precondition for the rise of #
# technolife on a planet is a climate a #
# thousand times more variable than normal, #
# so as to saturate the adaptive capacity #
# of DNA evolution and open a window for the #
# success of culture-based adaptation. #
How weird is that?
Brick: Complete absence of
large predators and herbivores
Kids love dinosaurs. In contrast to today’s
sedate, normal world, they present us with
this vision of a time in the distant past
when giants and titans struggled for control
of the land.
But, again, from an analytical point of view,
that is exactly backwards.
The dinosaurs didn’t live in a time of unusually
big predators and herbivores. The dinosaur era
was in fact quite unremarkable in that respect —
it represented the normal state of affairs.
Rather, -we- live in a peculiar large-animal vacuum.
When the Big Rock hit sixty-five million years
IT KILLED EVERY LAND ANIMAL ON
THE PLANET LARGER THAN A RAT.
Think about that. Let it sink in. Maybe it
will help to note that the Big Rock also
KNOCKED DOWN EVERY TREE ON THE PLANET. Which
trees then all burned, in the mother of all
forest fires. Imagine news helicopters sending
back video of THAT!
This wasn’t life as usual — this was very nearly
the end of metazoan life as we know it. In a
geological instant, ALL the large-animal
ecological niches were swept clean.
Predators, prey, runners, walkers, flyers —
The entire animal world had to evolve back
starting with nothing but rats and lizards.
SIXTY-FIVE MILLION YEARS JUST ISN’T
LONG ENOUGH FOR A JOB THAT BIG.
Biologically, we’re living in an era where the
biosphere is still recovering from the K/T
The rats are radiating out to fill the ecologinal
niches swept clean by the K/T Event, but the
process is far from complete.
In fact, it is really just getting properly
What is an elephant?
An elephant is a rat doing its best to be
Even the most cursory comparison of the two
will show how laughably far elephants fall
short of the real thing.
From a cosmic perspective, the entire animal
world today is just a weird giggle — teeny
tiny rats playing make-believe Big Animal in
ecological niches to which as yet they simply
aren’t adapted, amateurs more or less succeeding
in the Big Time because they don’t have to
compete with the professionals.
Its as though the TV networks and movies were
run exclusively by kindergartners because two
years ago a plague killed off everyone over
the age of four.
What does this have to do with the rise of
human civilization — with the appearance
of technolife on this planet?
HUMAN CIVILIZATION COULD ONLY
ARISE IN A LARGE-ANIMAL VACUUM.
Modern humans armed with flint warheads and
wooden missiles were barely able to cope with
runty little mastodons and cave bears.
They wouldn’t have had a ghost of a chance
against tyrannosaurs and brontosaurs.
Can you imagine Plains Indians or African
tribes setting up tents by the river in the
dinosaur era? The first T Rex to come along
would think that someone had spread out a
picnic meal for him! End Of Village.
Yet settled life is a prerequisite for the rise of
a civilization — you can’t develop agriculture,
architecture, and metal smelting while hiding in
the treetops and sneaking down at night to
Even ignoring the predator problem: Can you
imagine the first human farmers trying to make a
living from primitive barely-domesticated barley
in an era when entire herds of brontosaurus sized
herbivores could wipe out a year’s crop in minutes?
What was the farmer going to do — post KEEP OUT signs?
Build stone walls thirty feet high and thick?
Even the BIRDS were too big. This week’s
news includes a scientific paper concluding
that eagles were in the habit of killing and
eating human children, early in human evolution:
Wounds in child skulls from the era match eagle
beaks and eagle killing tactics.
If teeny little eagles could do that, can you
imagine what toothed flying critters with
forty-foot wingspans would have thought if THEY
caught a band of early humans in the open?
The simple fact of the matter is that man is
master of his world only because the previous
owners vacated the premises before he arrived.
He didn’t subdue the Earth — he inherited it
from a rich uncle, through sheer dumb luck.
HUMAN CIVILIZATION AROSE DURING A PERIOD OF
LILLIPUTIAN ANIMAL LIFE BECAUSE IT HAD TO —
HUMANS COULDN’T HAVE SURVIVED IN AN ERA
WITH NORMAL SIZED ANIMALS.
# A necessary precondition for the rise of #
# technolife is a convenient disaster which #
# kills off ALMOST all animal life on the #
# planet — but not ALL of it, or there’d #
# be nothing to evolve into humans. #
How weird is that?
 “Serenity”, by Joss Whedon
 Robert A Heinlein
Earth: A Borderline Planet For Life?
ScienceDaily (Jan. 14, 2008) ? Our planet is changing before our eyes,
and as a result, many species are living on the edge. Yet Earth has
been on the edge of habitability from the beginning. New work by
astronomers at the Harvard-Smithsonian Center for Astrophysics shows
that if Earth had been slightly smaller and less massive, it would not
have plate tectonics – the forces that move continents and build
mountains. And without plate tectonics, life might never have gained a
foothold on our world.
“Plate tectonics are essential to life as we know it,” said Diana
Valencia of Harvard University. “Our calculations show that bigger is
better when it comes to the habitability of rocky planets.”
Plate tectonics involve the movement of huge chunks, or plates, of a
planet’s surface. Plates spread apart from each other, slide under one
another, and even crash into each other, lifting gigantic mountain
ranges like the Himalayas. Plate tectonics are powered by magma
boiling beneath the surface, much like a bubbling pot of
chocolate. The chocolate on top cools and forms a skin or crust, just
as magma cools to form the planet’s crust.
Plate tectonics are crucial to a planet’s habitability because they
enable complex chemistry and recycle substances like carbon dioxide,
which acts as a thermostat and keeps Earth balmy. Carbon dioxide that
was locked into rocks is released when those rocks melt, returning to
the atmosphere from volcanoes and oceanic ridges.
“Recycling is important even on a planetary scale,” Valencia
Valencia and her colleagues, Richard O’Connell and Dimitar Sasselov
(Harvard University), examined the extremes to determine whether plate
tectonics would be more or less likely on different-sized rocky
worlds. In particular, they studied so-called “super-Earths”-planets
more than twice the size of Earth and up to 10 times as massive. (Any
larger, and the planet would gather gas as it forms, becoming like
Neptune or even Jupiter.)
The team found that super-Earths would be more geologically active
than our planet, experiencing more vigorous plate tectonics due to
thinner plates under more stress. Earth itself was found to be a
borderline case, not surprisingly since the slightly smaller planet
Venus is tectonically inactive.
“It might not be a coincidence that Earth is the largest rocky planet
in our solar system, and also the only one with life,” said Valencia.
Exoplanet searches have turned up five super-Earths already, although
none have life-friendly temperatures. If super-Earths are as common as
observations suggest, then it is inevitable that some will enjoy
Earth-like orbits, making them excellent havens for life.
“There are not only more potentially habitable planets, but MANY
more,” stated Sasselov, who is director of the Harvard Origins of Life
In fact, a super-Earth could prove to be a popular vacation
destination to our far-future descendants. Volcanic “rings of fire”
could span the globe while the equivalent of Yellowstone Park would
bubble with hot springs and burst with hundreds of geysers. Even
better, an Earth-like atmosphere would be possible, while the surface
gravity would be up to three times that of Earth on the biggest
“If a human were to visit a super-Earth, they might experience a bit
more back pain, but it would be worth it to visit such a great tourist
spot,” Sasselov suggested with a laugh.
He added that although a super-Earth would be twice the size of our
home planet, it would have similar geography. Rapid plate tectonics
would provide less time for mountains and ocean trenches to form
before the surface was recycled, yielding mountains no taller and
trenches no deeper than those on Earth. Even the weather might be
comparable for a world in an Earth-like orbit.
“The landscape would be familiar. A super-Earth would feel very much
like home,” said Sasselov.
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.
This research was the subject of a press conference at the 211th
meeting of the American Astronomical Society.
You have to not accidentally go extinct. A population of animals as large as
humans on a planet as small as the Earth has a substantial probability
of going extinct due to random population fluctuations.
For two-thirds of its history, Homo sapiens lived exclusively in
Africa. Only now are the details of that period becoming clear
MITOCHONDRIAL DNA is a remarkable thing. Itself the remnant of a
strange evolutionary event (the merger of an ancient bacterium with
the cell ancestral to all plant and animal life), it also carries the
imprint of more recent evolution. In many species, humans included, it
passes only from mother to child. No paternal genes get mixed into
it. That makes it easy to see when particular genetic mutations
happened, and thus to construct a human family tree.
The branches of that tree are now well studied. Humans started in
Africa, spread to Asia around 60,000 years ago, thence to Australia
50,000 years ago, Europe 35,000 years ago and America 15,000 years
ago. What have not been so well examined, though, are the tree’s
African roots. The genetic diversity of Africans probably exceeds that
of the rest of the world put together. But the way that diversity
evolved is unclear.
A study carried out under the auspices of the Genographic Project,
based in Washington, DC, and just published in the American Journal of
Human Genetics, goes some way towards correcting this oversight. The
study’s researchers, led by Doron Behar of the Rambam Medical Centre
in Haifa and Spencer Wells of America’s National Geographic Society,
have used the mitochondrial DNA of more than 600 living Africans to
show how genetic diversity has developed in Africa. In doing so, they
have shed light on how modern man spread around his home continent
long before he took the first, tentative steps into a bigger, wider
By the drought divided
The team paid particular attention to samples taken from the Khoi and
San people of southern Africa. These people, known colloquially as
bushmen, traditionally make their livings by hunting and
gathering. Indeed, their way of life is thought by many
anthropologists to resemble quite closely that of pre-agricultural
people throughout the world.
Comparing Khoi and San DNA with that of other Africans shows that the
first big split in Homo sapiens happened shortly after the species
emerged, 200,000 years ago. Most people now alive are on one side of
that split. Most bushmen are on the other. The consortium’s analysis
of which DNA ?matrilines? are found where suggests that for much of
its history the species was divided into two isolated populations, one
in eastern Africa and one in the south of the continent, that were
defined by this split. However, few other matrilineal splits from the
first 100,000 years of the species’s history have survived to the
This suggests the early human population was tiny (so the
opportunities for new matrilines to evolve in the first place were
limited) and reinforces the idea that Homo sapiens may have come close
to extinction (eliminating some matrilines that did previously
exist). Indeed, there may, at one point, have been as few as 2,000
people left to carry humanity forward.
This shrinkage coincides with a period of prolonged drought in eastern
Africa, and was probably caused by it. The end of the drought,
however, was followed by the appearance of many new matrilines that
survive to the present day. The researchers estimate that by
60,000-70,000 years ago, the period when the exodus that populated the
rest of the world happened, as many as 40 such groups were flourishing
in Africa?though that migration involved only two of these groups.
The African matrilines, however, seem to have remained isolated from
each other for tens of millennia after the exodus. It was not until
40,000 years ago that they began to re-establish conjugal relations,
possibly as a result of the technological revolution of the Late Stone
Age, which yielded new and more finely crafted tools. Only the bushmen
seem to have missed out on this panmictic party. They were left alone
until a few hundred years ago, when their homelands were invaded from
the north by other Africans and from the south by Europeans. Panmixis
thus came full circle. And that particular party was certainly not a
Sun’s Movement Through Milky Way Regularly Sends Comets Hurtling,
Coinciding With Mass Life Extinctions
ScienceDaily (May 2, 2008) ? The sun’s movement through the Milky Way
regularly sends comets hurtling into the inner solar system —
coinciding with mass life extinctions on earth, a new study
claims. The study suggests a link between comet bombardment and the
movement through the galaxy.
Scientists at the Cardiff Centre for Astrobiology built a computer
model of our solar system’s movement and found that it “bounces” up
and down through the plane of the galaxy. As we pass through the
densest part of the plane, gravitational forces from the surrounding
giant gas and dust clouds dislodge comets from their paths. The comets
plunge into the solar system, some of them colliding with the earth.
The Cardiff team found that we pass through the galactic plane every
35 to 40 million years, increasing the chances of a comet collision
tenfold. Evidence from craters on Earth also suggests we suffer more
collisions approximately 36 million years. Professor William Napier,
of the Cardiff Centre for Astrobiology, said: “It’s a beautiful match
between what we see on the ground and what is expected from the
The periods of comet bombardment also coincide with mass extinctions,
such as that of the dinosaurs 65 million years ago. Our present
position in the galaxy suggests we are now very close to another such
While the “bounce” effect may have been bad news for dinosaurs, it may
also have helped life to spread. The scientists suggest the impact may
have thrown debris containing micro-organisms out into space and
across the universe.
Centre director Professor Chandra Wickramasinghe said: “This is a
seminal paper which places the comet-life interaction on a firm basis,
and shows a mechanism by which life can be dispersed on a galactic
The paper, by Professor Napier and Dr Janaki Wickramasinghe, is to be
published in the Monthly Notices of the Royal Astronomical Society.
Solar System Is Pretty Special, According To New Computer Simulation
ScienceDaily (Aug. 8, 2008) Prevailing theoretical models
attempting to explain the formation of the solar system have assumed
it to be average in every way. Now a new study by Northwestern
University astronomers, using recent data from the 300 exoplanets
discovered orbiting other stars, turns that view on its head.
The solar system, it turns out, is pretty special indeed. The study
illustrates that if early conditions had been just slightly different,
very unpleasant things could have happened — like planets being
thrown into the sun or jettisoned into deep space.
Using large-scale computer simulations, the Northwestern researchers
are the first to model the formation of planetary systems from
beginning to end, starting with the generic disk of gas and dust that
is left behind after the formation of the central star and ending with
a full planetary system. Because of computing limitations, earlier
models provided only brief glimpses of the process.
The researchers ran more than a hundred simulations, and the results
show that the average planetary system’s origin was full of violence
and drama but that the formation of something like our solar system
required conditions to be “just right.”
The study was recently published in the journal Science.
Before the discovery in the early 1990s of the first planets outside
the solar system, our system’s nine (now eight) planets were the only
ones known to us. This limited the planetary formation models, and
astronomers had no reason to think the solar system unusual.
“But we now know that these other planetary systems don’t look like
the solar system at all,” said Frederic A. Rasio, a theoretical
astrophysicist and professor of physics and astronomy in
Northwestern’s Weinberg College of Arts and Sciences. He is senior
author of the Science paper.
“The shapes of the exoplanets’ orbits are elongated, not nice and
circular. Planets are not where we expect them to be. Many giant
planets similar to Jupiter, known as ‘hot Jupiters,’ are so close to
the star they have orbits of mere days. Clearly we needed to start
fresh in explaining planetary formation and this greater variety of
planets we now see.”
Using the wealth of exoplanet data collected during the last 15 years,
Rasio and his colleagues have been working to understand planet
formation in a much broader sense than was possible
previously. Modeling an entire planetary system — the varied physical
phenomena associated with gas, gravity and grains of material, on such
a variety of scales — was a daunting challenge.
The work required very powerful computers. The researchers also had to
judiciously decide what information was important and what was not, so
as to speed up the calculations. They decided to follow the growth of
planets, the gravitational interaction between planets, and the whole
planetary system in its entire spatial extent. They chose not to
follow the gas disk’s fluid dynamics in fine detail, but rather more
generally. As a result, they were able to run simulations spanning a
planetary system’s entire formation.
The simulations suggest that an average planetary system’s origin is
extremely dramatic. The gas disk that gives birth to the planets also
pushes them mercilessly toward the central star, where they crowd
together or are engulfed. Among the growing planets, there is
cut-throat competition for gas, a chaotic process that produces a rich
variety of planet masses.
Also, as the planets approach each other, they frequently lock into
dynamical resonances that drive the orbits of all participants to be
increasingly elongated. Such a gravitational embrace often results in
a slingshot encounter that flings the planets elsewhere in the system;
occasionally, one is ejected into deep space. Despite its best efforts
to kill its offspring, the gas disk eventually is consumed and
dissipates, and a young planetary system emerges.
“Such a turbulent history would seem to leave little room for the
sedate solar system, and our simulations show exactly that,” said
Rasio. “Conditions must be just right for the solar system to emerge.”
Too massive a gas disk, for example, and planet formation is an
anarchic mess, producing “hot Jupiters” and noncircular orbits
galore. Too low-mass a disk, and nothing bigger than Neptune — an
“ice giant” with only a small amount of gas — will grow.
“We now better understand the process of planet formation and can
explain the properties of the strange exoplanets we’ve observed,” said
Rasio. “We also know that the solar system is special and understand
at some level what makes it special.”
“The solar system had to be born under just the right conditions to
become this quiet place we see. The vast majority of other planetary
systems didn’t have these special properties at birth and became
something very different.”
In addition to Rasio, other authors of the Science paper are Edward
W. Thommes, an adjunct professor at the University of Guelph in
Ontario, former postdoctoral fellow at Northwestern and lead author,
and Soko Matsumura, a postdoctoral fellow at Northwestern.
The computer simulations were performed on a supercomputing cluster
operated by Northwestern’s Theoretical Astrophysics Group and
partially funded by a Major Research Instrumentation grant from the
National Science Foundation (NSF). Rasio’s research group on
exoplanets also is funded by a grant from the NSF Division of Astronomy.