Constraining the oxygen history of Earth's middle years using redox sensitive tracers

点击翻译按钮获取中文摘要

Reconstructing past oxygen: Sedimentary rocks, if interpreted correctly, can provide a timeline of the tumultuous oceanic and atmospheric conditions on the evolving Earth. The first long-lived accumulation of atmospheric oxygen began ~2.4 billion years ago (Ga), classically known as the Great Oxidation Event. Although this event has been documented for some time, mounting evidence points to more dynamic oxygen trends than previously thought. High oxygen levels at this time are implied by several lines of evidence, including high, modern-like concentrations of elements sensitive to oxidation and reduction (redox) reactions and high organic carbon in marine shales. Recent research shows a reversal of these oxygenation trends after ~2.05 Gacontrary to a long-held view that oxygen increased with time. This de-oxygenation event is poorly-resolved, but might provide important links to understanding how surface conditions were inadequate for complex biological evolution. It could also provide analogues for rapid changes in ocean chemistry reminiscent of that attendant with modern climate change.***Objectives: My research program aims to reveal the early developmental stages of the air we breathe. This research integrates advanced analytical techniques that address globally significant questions, including the causes and consequences of Earth's fledgling surface oxygen conditions. A robust record of oxygen history provides insight into the co-evolution of life or impediments to it. “Chicken and egg” arguments remain in the literature regarding the cause and effect of atmospheric oxygen rise, global glaciations, and biological evolution, including the advent of oxygenic photosynthesis.*** ***Scientific Approach: Past environmental conditions will be reconstructed using complementary geochemical methods, including isotopes of uranium, chromium, and molybdenum, coupled with redox-sensitive element concentrations. This research will track early oxygen conditions using these tools to illuminate the extent of anoxic conditions in ocean waters. Stratigraphic and radiometric dating methods will help determine the rate and timing of these changes.***Impact: The Earth system experienced a major disturbance that derailed a trend towards modern-like environmental conditions, but possible mechanistic explanations for this reversal are lacking. This research will investigate hypotheses related to both increasing and decreasing oxygen trends and concentrations of bioavailable elements in the oceans during key times in the geologic past. Piecing together Earth's path to its current oxygenated state is pivotal to unraveling biogeochemical feedbacks in the Earth system. Feedback mechanisms in past oceans have the potential to provide insights into the long-term consequences of modern-day oxygen-starved ocean waters that are increasing in conjunction with modern climate change. **