The preservation, distribution, and detectability of lipid biomarkers in the Atacama desert and implications for Mars
Wilhelm, Mary Beth
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Desert environments on Earth are colonized by organisms adapted to desiccation. We hypothesized that extreme and prolonged dryness might impart too great a challenge for microbial survival. To test this, we surveyed biomolecular proxies for soil microorganism activity across a steep rainfall gradient from the driest region within the Atacama Desert in Chile that receives just a few millimeters of precipitation per decade to a few millimeters a year. Lipid biomarker proxies for membrane response to environmental stress, degree of amino acid racemization, integrity of stress proteins suggest that organisms in the driest soils in the Atacama are not or very minimally metabolically active. While dry Atacama soils in this region might not be habitable, we found that dryness leads to greater preservation of biomarkers. Lipids from soil horizons in a 2.5 m vertical profile in the Yungay region were extracted and analyzed using GC-MS and LC-MS. Buried clay units were found to contain 40,000 year old-2 My lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains. We then took advantage of the above-mentioned characterized Atacama soil samples to assess the organic detection capability of current and future Mars mission flight-instrumentation including Raman laser spectroscopy and evolved gas analysis. Our data implies that Mars surface soils are too dry to support microbial life, but lipid biomarkers generated during a wetter epoch could be well preserved by hyperaridity if protected from other degradative processes.