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

重建过去的氧气：沉积岩，如果解释正确，可以提供地球演化过程中混乱的海洋和大气条件的时间轴。第一次长期的大气氧积累开始于约24亿年前（Ga），经典地称为大氧化事件。尽管这一事件已经被记录了一段时间，但越来越多的证据表明，氧气的变化趋势比以前认为的更加动态。这一时期的高氧水平由几方面的证据所暗示，包括对氧化和还原（氧化还原）反应敏感的元素的高浓度，以及海洋页岩中的高有机碳。最近的研究表明，在~2.05 g0之后，这些氧合趋势发生了逆转，这与长期以来认为氧随时间增加的观点相反。这个脱氧事件尚未得到很好的解决，但可能为理解地表条件如何不足以进行复杂的生物进化提供了重要的联系。它还可以为海洋化学的快速变化提供类似物，让人想起现代气候变化带来的变化。目的：我的研究项目旨在揭示我们呼吸的空气的早期发育阶段。这项研究整合了解决全球重大问题的先进分析技术，包括地球初生的表面氧气条件的原因和后果。氧气历史的可靠记录提供了对生命共同进化或阻碍生命共同进化的见解。“先有鸡还是先有蛋”的争论仍然存在于文献中，涉及大气含氧量上升、全球冰期和生物进化（包括含氧光合作用的出现）的原因和影响。*** ***科学方法：将使用互补的地球化学方法重建过去的环境条件，包括铀、铬和钼的同位素，以及氧化还原敏感元素的浓度。这项研究将利用这些工具追踪早期的氧气条件，以阐明海水缺氧条件的程度。地层学和放射性测年法将有助于确定这些变化的速率和时间。***影响：地球系统经历了一次大的扰动，偏离了向现代环境条件发展的趋势，但缺乏对这种逆转的可能的机制解释。这项研究将调查在地质历史的关键时期海洋中氧气增加和减少的趋势和生物可利用元素浓度的假设。拼凑出地球目前氧化状态的路径对于解开地球系统中的生物地球化学反馈至关重要。过去海洋的反馈机制有可能为了解与现代气候变化一起增加的现代缺氧海水的长期后果提供见解。**

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. **