Cryptoendolithic microorganisms colonize the upper few millimeters of limestone rocks of the Antarctic desert. These microbes live in a critically extreme environment, near the absolute limit of their physiological potential. Water from snowmelt and light penetrate the rocks but growth appears to be limited by the extreme low ambient temperatures. A climatic gradient has been observed to span a range of sites located in the McMurdo Dry Valleys. This study will quantify environmental conditions. Automatic data loggers will monitor the microscale climate inside rocks, and computer models based on these measurements will help identify the exact environmental threshold between life and extinction. Transmission electron microscopy will be used to document the degradation of dead communities and the formation of trace fossils. The communities studied here have been proposed as a terrestrial model for the last stages of life on early Mars. The results of these studies will serve to reconstruct the process of extinction on Mars and suggest the form its present- day traces might take. This project is jointly supported by the National Science Foundation and the National Aeronautics and Space Administration.
