Early Mars and early Earth: paleoenvironments for the emergence of life

摘要

There are good reasons to believe that environmental conditions on the martian surface during the first 500 million years (Ma) of its history were dramatically different from those at present. At or before the time at which the early Earth first supported both liquid water and life, before 3850 Ma, Mars apparently underwent erosional processes that strongly suggest a warmer, wetter climate and an operating hydrologic cycle. Martian life may have later become extinct as surface conditions gradually became intolerable, primarily due to atmosphere loss. If it is assumed that life is a "cosmic imperative", constrained by appropriate environmental conditions conducive to the stability of liquid water, it becomes logical to extend the search for geochemical evidence of past life on the ancient martian surface; a surface that is as old or older than die oldest rocks on Earth. The search for traces of such life via sample return missions from Mars could be focused on investigating the chemofossil record in ancient water-lain sediments such as paleo-lake beds, fossil hydrothermal fields, and stream channels. Alternatively, martian organisms could have disappeared into the crust, sequestered in discrete P-T microenvironments where liquid water remains stable. Such environments would include deep hydrothermal systems and groundwater aquifers; perhaps such regions continue to support organisms up to the present time.