Biology and the exploration of Mars

Knowledge of Mars based on the findings of two Viking landers during 1976 and 1977 is reviewed. The most significant observation was the absence of any detectable organic compounds at the two landing sites. Viking did indicate, however, that the surface contained unidentified strong oxidant(s) that could account for the absence of organics. Consideration has been given to the possibility that chemical evolution on Mars produced living organisms under earlier, more benevolent conditions, but these organisms could not adapt to worsening conditions over geologic time and became extinct.