Abstract

Photosynthetic microbes have converted the light energy into the chemical energy of organic carbon and oxidized compounds such as oxygen for billions of years. Early on, these microbes are thought to have used sulfide, reduced iron and organic compounds as electron donors for carbon fixation. Water-splitting, oxygen-producing photosystems evolved later and irretrievably changed the compositions of ecosystems, surface rocks, water bodies, and the atmosphere. When and how this happened are still major questions in Earth history, biology, geochemistry and planetary evolution. My laboratory addresses these questions by asking how microbial behaviors, metabolisms and fossilization processes shaped the sedimentary record. Our work uses experiments to probe the preservation potential of different microbial communities, compares experimental results to the actual record, and identifies trends in the record that can be best explained by either oxygen-producing or anoxygenic photosynthesis. Combined information from experiments, modern genomes of oxygen-producing microbes and the very long fossil record of the same microbes is combined and used to calibrate molecular clock models and time the origin and events in the evolution of oxygenic photosynthesis in deep time.