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Project Progress

Organic Molecules as Biosignatures (dm)

We have continued our study of the temperature and environmental history of Siberian permafrost core samples, from which viable bacteria apparently several million years in age have been isolated. Our data clearly show that the rate of aspartic acid racemization below approximately 5 m, or about 20000 years in age, has been consistent with the measured temperature of the permafrost. This indicates that there has been little or no metabolic activity in the organisms below 5 m. In contrast, the organisms present from the surface down to 5 m have clearly warmed sufficiently to metabolize D-amino acids and thus partially reset the racemization “clock”. This study demonstrates the usefulness of amino acid racemization as an in situ indicator of metabolic activity in cold environments.

We are also still studying the fate of organic material produced by cryptoendolithic organisms colonizing Antarctic dry valley sandstone. Soluble organics, including amino acids, are transported into the interior of the rock by small flows of snowmelt. The amino acids in the rock interior show significant amounts of racemization, suggesting that they have been in the interior for long periods of time. We are currently comparing the amount of organic carbon lost by the cryptoendolithic community into the rock interior with the amount used in the production and secretion of iron-mobilizing agents. This will allow us to more closely constrain and better understand the metabolic cost that these organisms must pay in order to survive in the dry valley environment.

We have also used experimentally determined rate constants for aspartic acid racemization in Siberian permafrost sediments, combined with temperature vs. latitude data from Mars Global Surveyor, to calculate the range of latitudes on Mars over which a biological chiral amino acid signature would survive throughout the planet’s history. We find that such a signature should be detectable in samples collected at latitudes poleward of approximately 30â?? and from depths of at least 1-2 meters.