Life on Mars: how it disappeared (if it was ever there).

The cryptoendolithic microbial community in the Ross Desert (McMurdo Dry Valleys) of Antarctica exists at temperatures significantly below the temperature optima of the primary producers. Surviving near the limit of their physiological adaptability, the organisms are under severe environmental stress, so further deterioration in the environment results in cell damage and death. The sequence of events leading to extinction is considered to be a terrestrial analog for disappearance of possible life on early Mars. Progressive stages of cell damage and death in the Ross Desert material are documented with transmission electron microscopy.