From: LARRY KLAES (ljk4_at_msn.com)
Date: Sun Mar 07 2004 - 09:56:25 PST
How the Little Green Men Met Their Makers
March 7, 2004
By KENNETH CHANG
NOW that there's conclusive evidence that at least part of
Mars was once a water-soaked place where living things
could have wriggled, swam or slithered, it takes only a few
more leaps of speculation to wonder how they might have
died.
Did their eyes bug out like Arnold Schwarzenegger's in
"Total Recall"? Not likely - hypothetical Martian creatures
probably wouldn't have had enough time to evolve eyes
before the planet became the cold and arid place it is
today.
In the optimistic picture of life on Mars, a thick blanket
of carbon dioxide created a greenhouse effect that warmed
the planet for its first billion years or so, and lakes and
oceans dotted the surface. (The pessimistic view is that it
was always cold and lifeless.)
But for at least 500 million years, Mars, like Earth,
endured a period known as "heavy bombardment," when it was
repeatedly whacked by meteors large enough to vaporize the
oceans.
Life probably wouldn't have had enough time to gain a
foothold between impacts, and even if it had, it would have
been boiled and steamed to oblivion by the next meteor.
Thus, life on Mars would likely have had, at best, a run of
a few hundred million years.
Even so, some scientists speculate that life could have
been more precocious on Mars than on Earth. Life on Earth
started between 3.9 billion and 3.5 billion years ago.
Mars, only half as wide as Earth and with only one-tenth
its mass, would have been a smaller target for meteors and
might have become habitable sooner.
In addition, Mars doesn't have plate tectonics, and some
scientists have argued that the lack of movement in the
planet's crust could have led to a different chemistry in
the air and rocks, leading to an early build-up of oxygen
produced by the photosynthesis of plants.
While life remained stuck at the single-celled level for a
billion years on an oxygen-poor Earth, evolution on Mars
might have led much more quickly to microscopic animals.
But then, about 3.5 billion years ago, the planet turned
chilly, and the Martians - if they ever existed - would
have been snuffed out in any of several ways:
They froze. Most of the planet's carbon dioxide either
leaked into space or was permanently transformed, via
chemical reactions, into rock. On Earth, through plate
tectonics, whatever rock goes down comes back up through
volcanoes, and the carbon dioxide is returned to the air.
On Mars, it's a one-way street, and its carbon dioxide,
locked into place, disappeared from the air.
As the carbon dioxide vanished, so did the greenhouse
effect. As a result, Mars today is like an Antarctica
without an atmosphere.
They dried up. Even at Meridiani Planum, the place where
scientists said last week the Mars rover Opportunity had
found evidence of "soaked" rocks, the discovery of vast
quantities of sulfur salts suggests the former presence of
a wet area like a lake that dried up.
They suffocated. If Martian life reached the animal level,
with creatures able to live off oxygen produced by plants,
they died off as the plant life dried up or froze. Kill off
Earth's plant life, and animals here would run out of stuff
to breathe, too.
They starved. As the planet's flowing water froze or dried
up, Martian microbes chomped up all the available food.
"You need phosphate," said Dr. Andrew Knoll of Harvard
University. "You need nitrogen. It's not clear to me that
biologically useful forms of those nutrients would be
abundant."
They were fried. Mars does not have a magnetic field to
deflect the solar wind, and its thin atmosphere does not
block out ultraviolet light. Thus, Martian organisms were
done in by sunburn and cancer.
They went underground. The truly optimistic say life could
persist underground on Mars, just as microbes fill the top
few miles of Earth's crust. The overlying soil would
protect them from the cosmic and ultraviolet radiation, and
liquid water would be available from underground ice melted
by heat from the interior. "It could easily have migrated
to the subsurface and exist today," said Dr. Bruce Jakosky,
a professor of geological sciences at the University of
Colorado.
They are us. Billions of pieces of Mars, blasted into space
by meteors, have landed on Earth. Scientists have shown
that the interior of a Martian meteorite found in
Antarctica never reached temperatures hot enough to kill
bacteria.
If life actually did arise on Mars, then at least some
Martians possibly made it here.
At least one species of earthly bacteria, Bacillus
subtilis, is capable of surviving the rigors of space
travel. In one experiment, 10 percent of this species sent
into orbit on a satellite survived six years in the vacuum
of space. Other experiments show that Bacillus subtilis, as
well as another common bacterium, Deinococcus radiodurans,
can also survive the tremendous jolt of being blasted into
space by a meteor - up to 100,000 times the normal pull of
gravity on Earth - as well as the bombardment of cosmic
radiation during the trip.
In a Martian rock that originally carried a few million
microbes, a 10 percent survival rate would still leave a
few hundred thousand Martian microbes to populate Earth.
Or maybe there never were native Martians or Earthlings at
all, and life originated from a third planet.
"We can always blame it on Venus,'' Dr. Jakosky said.
http://www.nytimes.com/2004/03/07/weekinreview/07mars.html?ex=1079681890&ei=1&en=bf2f1464572159a5
This archive was generated by hypermail 2.1.6
: Sun Mar 07 2004 - 10:05:18 PST