Biosignatures of microbial function in subsurface systems

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Microbial organisms were the first and remain the most prolific forms of life on Earth, and are thought to be the most likely form of life to be observed in the search for life beyond the Earth. Understanding the unique organic, isotopic, mineral or morphologic biosignatures associated with microbial life in extreme environments provides the foundation for our interpretation of the history of life on Earth recorded in the geologic record, as well as the basis by which we will search for life on Mars or elsewhere. While estimated to be comparable in mass to that on Earth’s surface, the subsurface biosphere is only recently being explored. This proposal seeks to understand the carbon sources, metabolic activities and biosignatures associated with life in the deep terrestrial subsurface, and to compare and contrast it with those of endolithic communities living just below the surface of rocks in extreme environments. Taking advantage of ongoing research and relationships with working mines, this research will sample fracture systems that range from paleometeoric, biological systems isolated for thousands to millions of years at shallower depths to ancient, deeper systems that have been isolated for up to more than a billion years and may preserved abiotic signatures comparable to the early Earth and meteorites. Biosignatures of bacteria, eukarya and archea, as well as signatures of bacterial spore formation will be analyzed across these systems to assess the microbial community including the distribution of microbial abundance, the carbon sources and cycling that is supporting it, and the limits on its persistence along with the extent to which it is a dynamic system over geologic timescales. Recognizing and interpreting evidence of the activities of microbial life, both on Earth and potentially beyond, also requires the ability to differentiate unique “biosignatures” of life and its processes from signatures of abiotic systems (“abiosignatures”). While life has overprinted any abiotic signatures in almost all environments on Earth, some of these deep fracture systems, especially the most ancient ones, may in fact sample abiotic conditions and thus provide an unparalleled opportunity to characterize “abiosignatures” on Earth. These abiosignatures could then be compared to those associated with meteorites and provide an exciting new perspective on the search for life beyond the Earth. In addition to field samples, microcosm experiments designed to characterize biosignatures of microbial utilization of energy and/or carbon sources generated via water rock interaction will be used generate an laboratory based dataset that will contribute to interpretation of field results. As a counter point to this deep subsurface system, a secondary research focus will be on endolithic communities living millimeters below the surface of rocks in surface environments under extremes of aridity, temperature and geochemistry. Understanding the abundance, metabolisms and persistence of these systems will contribute complimentary insight to the research in the deep subsurface, furthering our understanding of the limits and capabilities of life, as well as developing our understanding of biosignatures and their implications to the record of life in the geologic record of life on Earth and as targets for the search for life on other planets.