Bricks In The Wall:

Why we're alone in the galaxy

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.

Candidate Bricks

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.
(http://www.sciencedaily.com/releases/1999/11/991130065720.htm)

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:

http://www.nandotimes.com/newsroom/ntn/health/062698/health5_3819.html

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:

http://www.sciencedaily.com/story.asp?filename=980602080449

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.

Notes

I

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 :)

II

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?
http://www.canoe.ca/Catalyst/star_science.html

                        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
caused
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
over
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
absorbed
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
so
quickly after mass extinctions.
Those animals that survived -- because of their
hardiness or lack of radioactive exposure --
would have produced a greater number of
genetic
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
either
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."

III

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: http://www.nando.net/newsroom/ntn/health/052897/health31_9067.html 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 life on the planet, scientists reported on Wednesday. The snowballs are actually small comets about 40 feet in diameter, which appear to be streaking toward Earth in a steady stream. 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 theorized 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 immediately 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, or 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 said. But Frank said that over the course of billions of years, even this miniscule amount of water would be enough to fill all of Earth's oceans. The Polar satellite, which orbits high above the Arctic Circle, tracked the snowballs as they disintegrated, and using a filter that detects visible light emitted by water molecules, Frank determined 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.

IV

Another brick in the wall? Earth getting hit by something Mars-size and surviving was already a big brick in the wall: Now the impactor is three times the size of Mars. Yow! http://www.nando.net/newsroom/ntn/health/072897/health2_29216.html Study says moon formed by collision with giant planet 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 moon. 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 study 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 in our solar system and in solar systems that may exist around other stars." ----------------------------------------------------------------------- 97Oct03 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 alone. ----------------------------------------------------------------------- http://www.nando.net/newsroom/ntn/health/020598 Comets not the Earth's oceans only source of water: researchers 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 hypotheses that comets were the single source of water filling Earth's oceans, the journal Science reports. Astronomers have long considered comets a sort of fossil evidence of how the solar system was formed. And some have believed that the ice, dust and rocks in comet tails may have played a crucial role in the formation of the atmosphere of the planets, filling 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 --> -- hydrogen 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 water, or HDO, is considerably higher in the comet tails than in the Earth's oceans. "It appears that comets by themselves cannot be the only source of water for Earth's oceans," the authors concluded.

One more thing that can go wrong building an Earth:
http://www.sciencedaily.com/story.asp?filename=980309043643:


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
basalts.

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
rises instead.

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
thickens.."

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
two planets."

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
hotter then.

"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:

                                                                           Science Headlines 


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
equator.

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
time."

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
the stars.

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
for life.

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
there.

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:

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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.

AAAS Expo
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.

Sun facts
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.

Burnt-out planet

"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:
http://www.sciencedaily.com/releases/2000/03/000313081731.htm

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
Ecology Letters.

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
say.

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
lost.

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
Earth's surface.

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"
deadly.

But it will be the ultraviolet spring that helps finish off the
survivors.


Sounds like we're a bit lucky our beast isn't feeding:

http://www.sciencedaily.com/releases/2000/03/000322091619.htm
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
black holes.

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
close."

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
Martini.

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
galaxy.

"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:

http://www.sciencedaily.com/releases/2000/03/000329080630.htm

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
Earth.

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
years.

"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,
he said.

"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
Earth.

"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
lunar analysis."

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
To: cynbe@laurel.actlab.utexas.edu
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.

[...]

David Studhalter

The Radio Ionus News Service of Earth
(The 2000Jul Scientific American also notes that the Sun is
unusually metal-rich.)
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
used
the National Radio Astronomy Observatory 12-m radio telescope to scan
a huge molecular cloud only 30 light years from the
galactic center. 

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
material-processing objects. 

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
the
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.) 

2001-Feb-05:
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1154000/1154784.stm

"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."
2001-02-16:
http://www.cnn.com/2001/TECH/space/02/05/inbrief.020901/#1

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
said.

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
leaving Africa."

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
said.

"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
said.

 -- http://www.cnn.com/2001/TECH/science/04/20/human.origins.ap/index.html
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:

http://news.bbc.co.uk/hi/english/sci/tech/newsid_1298000/1298460.stm

    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
    have revealed.

    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
    Andes.

    Earth pyramids

    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.

    'Power'

    "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.


http://www.sciencedaily.com/releases/2001/05/010504083512.htm

              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
              planets. 

              "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
              erosive star-shine. 

              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.

Chaos theory

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
Earth-crossing orbits.

"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
their theory.

"At the moment the link with the dinosaurs is based on a coincidence
in time and a plausible mechanism," he added.

'Tenuous' link

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
doorstep."
http://www.abc.net.au/science/news/stories/s327749.htm

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"
to us.

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
there". 

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
outer crust.

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."

http://www.sciencedaily.com/releases/2002/01/020109074626.htm

Source:
                              
Johns Hopkins University (http://www.jhu.edu)

Date:

Posted 1/9/2002


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
Earth.

"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
Astronomical Society.

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
event.

"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
planet.

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.

http://news.bbc.co.uk/hi/english/sci/tech/newsid_1975000/1975354.stm

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
the ground.

Within moments of the arrival of the radiation from deep space, the
atmospheric temperature will begin rising rapidly, wreaking havoc with
global weather systems.

Destructive 'daughters'

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
come.

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
"daughter" particles.

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.

Threatening stars

"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
Earth.

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
our direction.

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."
http://www.space.com/scienceastronomy/astronomy/goldilocks_zone_020528-1.html

    Amid the Universe's Chaos, a Few Habitable Places

    By Robert Roy Britt Senior Science Writer posted: 07:00 am ET 28 May
    2002

    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
    all.

    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
    least.

    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
    biological evolution.

    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.

    Bully stars

    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
    spiral arms.

    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
    less.

    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
    form stars.

    "Nearby interactions with multiple stars in a rich cluster can
    truncate and even completely eliminate protoplanetary disks," Bally
    said.

    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
    planets."

    However, if a planet can form quickly -- and theorists are not sure
    just how long this process takes -- then the radiation is irrelevan