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 for longer.

It appears that it has been about one and half billion years since Mars lost the bulk of its atmosphere and since its water was globally trapped underground and at the poles. We suppose that volcanic activity 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.