SEARCHING FOR LIFE ON MARS: THE ROLE OF CALCIUM SULFATE IN RECORDING PAST BIOLOGICAL ENVIRONMENTS

One of Jack Farmer’s many research innovations was highlighting the importance of salts as sampling targets for life detection NASA missions. His career of work on evaporitic systems showed that salts, as well as ice, carbonates, and silicates, promote microbial fossilization, indicating they could potentially trap the record of life on other planets. However, to fully understand the interplay between calcium sulfates, biosignatures, and the past environment on Mars, we need to study similar systems on Earth. The goal of this research is to answer the question, “Is there variation in biosignature entrapment in gypsum?” Gypsum samples were collected from four sites: (1) Blaine Formation, KS (2) Lake Lucero, White Sands National Park, NM (3) South Bay Salt Works, San Diego, CA and (4) various salt lakes in Western Australia. These sites range in both geologic age (Permian-modern) and environment of precipitation (i.e. alluvial fan, ephemeral lake, salina, evaporative seaway). Analytical techniques including petrographic and fluorescence microscopy were used to target and identify potential biomarkers entrapped in the gypsum crystals. Upon comparison of the potential biomarkers present across all four locales, results showed three unique modes of entrapment- microbes within the crystal, microbes within fluid inclusions, or a microbial mass within the core of the crystal. There appeared to be no trend between age, environment of deposition, and mode of entrapment. This variety of biosignature entrapment shows the ability of gypsum to fossilize microbes across a range of environments, making it a useful tool for life detection.