Bio-markers and the search for extinct life on Mars.
Geologic and climatologic studies suggest that conditions on early Mars were similar to early Earth.  Because life on Earth is believed to have originated during this early period (3.5 billion years ago), the Martian environment could have also been conducive to the origin of life.  To investigate this possibility we must first define the attributes of an early Martian biota.  Then, specific geographic locations on Mars must be chosen where life may have occurred (i.e. areas which had long standing water), and within these distinct locations search for key signatures or bio-markers of a possible extinct Martian biota.  Some of the key signatures or bio-markers indicative of past biological  activity on Earth may be applicable to Mars including:  reduced carbon and nitrogen compounds, CO3(2-), SO4(2-), NO3-, NO2- [correction of NO2(2)], Mg, Mn, Fe, and certain other metals, and the isotopic ratios of C, N and S.  However, we must also be able to distinguish abiotic from biologic origins for these bio-markers.  For example, abiotically fixed N2 would form deposits of NO3- and NO2-, whereas biological processes would have reduced these to ammonium containing compounds, N2O, or N2, which would then be released to the atmosphere.  A fully equipped Mars Rover might be able to perform analyses to measure most of these biomarkers while on the Martian surface.
Schwartz
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DE
NASA-Ames Research Center, Solar System Exploration Branch, Moffett Field, CA 94035, USA.
Mancinelli
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RL
D005075:Biological Evolution; D002244:Carbon / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry; D018534:Earth, Planet; D018559:Exobiology; D005580:Fossils; D055593:Geological Phenomena; D005844:Geology; D018535:Mars; D008670:Metals / Q000737:chemistry; D017672:Nitrogen Compounds / Q000737:chemistry; D000069497:Origin of Life; D010163:Paleontology; D000644:Quaternary Ammonium Compounds / Q000737:chemistry
D008670:Metals; D017672:Nitrogen Compounds; D000644:Quaternary Ammonium Compounds; D002245:Carbon Dioxide; D002244:Carbon