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Our investigation in Mars-relevant terrestrial environments where biological material is entombed within rapidly precipitated evaporite crystals has given us the ability to evaluate the preservation potential of a hypersaline brine system in advance of interrogating similar environments on Mars. These evaporite minerals, halite (NaCl) and gypsum (CaSO 4 ), have been found to host authigenic fluid inclusions over geologic time, with cellular life and carotenoid pigments that are understudied in the planetary context. Great Salt Lake provides an excellent site to test the ability to detect organic matter in Mars-relevant evaporite crystals. DNA was extracted to determine which microbial clades were present and assess the attenuation of DNA preservation from the host fluid of the lake to the mineral. Raman spectroscopy was used to investigate the presence of pigments that have longer preservation potential than DNA. Compared with the water column, evaporite minerals preserve higher volumes of DNA and associated biochemistry, whereas entombed fluid inclusions preserve even higher magnitudes of both biomarkers. This indicates organic addition and continued preservation as the crystals precipitate from the fluid, which was later confirmed as micrometer-scale environments continued to maintain the ecology within closed-system fluid inclusions. Raman analyses of halite revealed the presence of β-carotene and bacterioruberin, consistent with the presence of carotenoid-generating bacteria and archaea in this hypersaline environment, which are characterized by pink coloration. The continued preservation of these chemical biomarkers over time has led to the formation of physical biosignatures within the evaporite record. Given that these same minerals are present in ancient fluvial sites across Mars, halite and gypsum are ideal candidates for future in situ observation and should be considered high priority for sample return missions.
Perl et al. (Sat,) studied this question.