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Forget
The Big Bang Know The Microbes
Paul
Davies
One
hundred years ago it was widely believed that
there was life on mars. The American astronomer
Percival Lowell even produced detailed maps of
canals he claimed had been constructed by
water-deprived Martians. Then in1960's space
probes sent to mars failed to reveal any sign of
life, let alone intelligent canal-building life.
But the coup de grace came in 1977 when the US
space agency NASA landed two Viking spacecraft
on the Martian surface with the specific aim of
searching for signs of biological activity. Not
so much as a bacterium was found. The surface of
mars appeared to be a freeze-dried desert,
utterly hostile to any form of life.
Today
this pessimistic assessment seems too hasty. I
believe not only that mars have harbored life,
but it may actually be the cradle of life. This
conclusion arises because of the recent
discovery that our biosphere extends deep in to
the bowels of the earth. Microbes have been
found thriving at depths of several kilometers,
inhabiting the pore spaces of apparent solid
rock. Genetic studies suggest these deep-loving
organisms are among the most ancient on the
planet. They are, in effect, living fossils.
Because
temperature sharply rises with depth, the
subterranean microbes tend to be extremely
heat-tolerant. There is, however, a limit. Mars
cooled quicker because it is smaller.
The comfort zone for deep living,
heat-tolerant microbes would have been deeper
sooner. All in all, the red planet offered a
more favorable habitat for life during the early
history of the solar system. We don’t know
where life began, but a kilometer or two below
the surface of Mars seems a good place. How,
then, did life get from Mars to Earth? The
answer is straightforward. The same asteroid
impacts that made early life so hazardous also
served to splatter vast quantities of Martian
rock around the Solar System. A fraction of this
hits Earth; indeed, it does so today. So far, a
couple of dozen meteorites have been found that
can be traced back to Mars.
If
there was life on Mars, then it is possible that
some Martian microbes will have hitched a ride
inside the ejected rocks and made their way to
earth. When I suggested this Idea about ten
years ago, few scientists took it seriously.
They found it incredible that any form of life
could survive being blasted off a planet and
subjected to the inhospitable environment of
outerspace. Yet evidence is steadily growing
that microbes could withstand the violence of
ejection, the savage radiation of interplanetary
space as well as the heat of atmospheric
re-entry.
Initially
Mars was the more bio-friendly planet; Earth was
a scalding hell. Once life got going on the Red
Planet, it quickly spread through the subsurface
zone – a good refuge from impacts. However,
those microbes living near ground zero of a
major impact would have been flung into orbit
round the sun. The lucky ones, buried deep
inside large boulders, could have survived in
space for millions of years. A few of those
boulders would, over such durations, hit the
earth. Although many microbes would perish in
space, and more would die on high-speed entry to
Earth’s atmosphere, it would take just one
viable organism to seed our planet with life.
One of the puzzles about life’s appearance on
Earth is that it happened so quickly after the
bombardment abated about 3.8 billion years ago.
There are distinct traces of life in Australia
dating from 3.5 billion years ago, and hints of
life in rocks from even earlier times. This is
readily explained if life came from Mars. We can
imagine a continuing rain of microbe-laden
Martian debris falling on Earth during
bombardment. As soon as conditions finally
settled down, these colonists would have
flourished. Martian life was probably
established itself here many times, only to be
destroyed by the next big impact. If I am right,
then you and I are the direct descendants of the
first Martians able to burrow hot and able to
burrow hot and deep, and ride out the remaining
fury of the cosmic bombardment.
SOURCE-The
Guardian, London
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smaller spacecraft, instead of one huge
expensive spacecraft. In this way, the
loss of one craft would not doom an entire
exploratory mission. The first in this
series of “Discovery missions” was Mars
Pathfinder. In contrast to the
billion-dollar Mars Observer mission,
Pathfinder was designed, built and
launched for only 250 million dollars,
one-fourth the cost of Observer.
Like Viking, Pathfinder included
a lander, but it also included something
never before attempted: an independent
rover, named Sojourner, capable of
traveling up to ten meters (32 feet) away
from the lander. The mission tested a
number of new technologies. Instead of
using a Viking-style retrorocket,
the Pathfinder lander was encased
in four large six-chambered air bags. Upon
entering the Martian atmosphere, the
lander parachuted most of the way to the
surface, then deployed and inflated its
air bags for landing. The spacecraft
bounced 15 to 20 times, sometimes as high
as 50 feet. The landing went exactly as
planned. On July 4, 1997,