Fe Isotopes and Biological Processing of Fe in the Pre-Oxygenated Earth: Archean to Mid-Proterozoic Banded Iron Formations

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9903252Johnson The proposed research will focus on using iron (Fe) isotopes to trace the role of microorganisms in the geochemical cycle of Fe in the Archean to Mid-Proterozoic, covering the earliest Earth (3.8 billion years ago), to a period of rapid change in atmospheric conditions about 2 billion years ago. Our goals are to develop an "isotopic fingerprint" that uniquely records biologic activity, but is relatively immune to later changes, such as alteration of rocks by younger geologic processes. The "isotopic fingerprint" will rely on the observation that microorganisms fractionate the relative abundances of the four stable isotopes of Fe (54Fe, 56Fe, 57Fe, and 58Fe) through selective preference for the lighter masses. We propose that the isotope composition of Fe will provide a powerful means to evaluate the role of microbes in the geochemical cycling of Fe in the Precambrian, which is critical for accurately interpreting Precambrian atmospheric conditions from the rock record.