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Geomicrobial dynamics and microbial metabolism influence biomarker preservation in actively lithifying hydrothermal environments
Rasmussen, Kalen L.
Rasmussen, Kalen L.
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2023
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2024-04-18
Abstract
Hydrothermal environments are potential locations for the origin of life and excel at lithifying and preserving the surrounding environment. The lithification of actively growing microbial mats in hydrothermal environments preserves information regarding the biological life inhabiting the ecosystem and environmental variables such as geochemistry and fluid flow. Lithified microbial mats enter the rock record as microfossils acting as ancient biosignatures, which are prime targets for elucidating details of Earth’s geobiological past and may potentially aid in the identification of life elsewhere. Studying modern hydrothermal analogue environments allows for intricate interactions between mineralogy, geochemistry, and microbiology to be untangled, facilitating more accurate interpretations of the rock record. This dissertation leverages two modern hydrothermal analogue environments located in Yellowstone National Park, USA to unravel the complex geomicrobial interactions that impact and result in the formation of geologically persistent biomarkers. The compounding variables impacting microbial mat lithification and biosignature preservation were deconvoluted by integrating nucleic acid sequencing, geochemical profiling, petrography, and lipids analysis. First, microbial communities in an actively lithifying ecosystem were determined to be dynamic and metabolically flexible despite stable geochemical conditions and niche competition, impacting broad interpretations of microbial life observed in the rock record. Next, living microbial communities’ structural, isotopic, and lipid biosignatures were characterized and disentangled from diagenetic influences and endolithic microbial community signals. Lastly, dissimilatory iron reduction coupled to photosynthesis was determined to be active in stromatolite forming microbial mats, acting as a novel lithification mechanism for stromatolite preservation. Together, these findings help clarify the microbiological impact on lithification in hydrothermal ecosystems, distinguish extinct and extant biosignatures at modern analogue sites, and aid in our search for life elsewhere by constraining legitimate microbiological signals.
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