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Oasis on Mars
Environmental conditions favorable for the evolution of life on
Mars may have occurred during the earliest period following planetary
accretion, a time known as the Noachian (Noachis is the names given
by classical astronomers to a region that we know today contains the
oldest terrain on Mars). Geologic mapping identifies a variety of
sites (such as valley outlets, topographic lows, depressions, and
basins) in the martian tropical zone where water would have drained
and perhaps been stable for hundreds of millions of years. We choose
to call these sites paleo-oases.
While the rate of change is quite uncertain we conclude that Mars
has evolved to colder and dryer conditions since the Noachian.
Cooling conditions by atmosphere loss would have had an impact on of
the paleo-oasis sites mentioned above. The global hydrologic regime
was evidently modified with time and volcanism became focused around
Tharsis and Elysium. The numerous episodic outflow flooding events
that took place over the billion years following the Noachian would
have created temporary lakes (or even small seas) at their outlets.
Such standing bodies of water (perhaps covered by permanent ice) may
have maintained the aqueous conditions necessary for biogenic
evolution or, if life had evolved earlier, may have sustained life
when surface conditions became too hazardous.
It appears that it has been about one and half billion years since
Mars lost the bulk of its atmosphere and ever since its water had
been globally trapped underground and at the poles. We suppose that
volcanic activity had also decreased. If life had not evolved by this
time then it seems unlikely that it would have done so subsequently.
If life had evolved it would have had a real challenge to find niches
to survive under conditions which today are extremely hostile to any
kind of organic molecules.
     
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