PhD, University of Cincinnati, 2024, Arts and Sciences: Geology

The Great Oxygenation Event is the period, between 2.3 and 2.4 billion years ago, when oxygen began to accumulate in Earth's atmosphere. It was arguably the most consequential change in the history of our planet and the life that inhabits it. Knowledge of the events that led to this change is of great scientific interest because it will help us understand how Earth became a planet that can support complex multicellular organisms, including humans, and determine what to look for when planning missions to seek evidence of life beyond Earth, such as NASA's current Mars 2020 mission. This dissertation presents studies of fossilized microorganisms (microfossils) and microbially-influenced carbonate (carbonate microbialites) that formed shortly before the Great Oxygenation Event. Three-dimensional reconstructions along with photomicrography reveal the morphologies and habits of the preserved microbial communities to provide a better understanding of the types of microorganisms that existed just before the Great Oxygenation Event. The results suggest that microorganisms may have evolved to take advantage of transient microoxic-sulfidic interfaces 200 million years before the Great Oxygenation Event. Petrographic examinations and Raman spectroscopy provide insight into the geological processes that led to the preservation of these microfossils and microbialites. Understanding the preservation and detection of life's signatures, or biosignatures, on Earth is both necessary to the study of life on Earth and foundational to planning missions to seek biosignatures elsewhere in the solar system. The results of this work include the first reported instance of early diagenetic silicification that occurred via silica spherule nucleation directly on organic matter in a deep-water environment. To support the interpretation of DUV Raman data collected on Mars, this dissertation presents a comparison of Raman data collected from terrestrial biogenic microbialites with a Mars 2020 analo (open full item for complete abstract)

Committee: Andrew Czaja Ph.D. (Committee Chair); Carlton Brett Ph.D. (Committee Member); Susannah Porter Ph.D. (Committee Member); Annette Rowe Ph.D. (Committee Member); Joshua Miller Ph.D. (Committee Member) Subjects: Paleontology