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Extreme Habitats

Fossil Biochemicals: Former Life on Mars and Other Terrestrial Bodies

Microbial communities themselves may not survive, but their fossil biochemicals may be preserved in frozen regolith. The survival of marker biomolecules for periods of geological time requires conditions which minimize their degradation by the attrition of internal molecular motion and damage by external radiation. Even in a highly desiccated state, gradual deterioration of macromolecules such as DNA and proteins at temperatures of ~20°C requires occasional periods of anabolic activity to repair the accrued damage.

Subzero temperatures reduce the rate of deterioration, but even in soils at temperatures below -20°C dormant microbes may require a pulse of growth-supporting conditions to effect biochemical repairs. This situation is alleviated in highly desiccated extremely cold conditions by the adsorption of biomolecules and cells onto mineral crystals which have been found to preserve the activity of immobilized enzymes such as nitrogenase after 1.8 Ga in Siberian permafrost soil.

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