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，可以提供一个时间轴动荡的海洋和大气条件的演变地球。大气中氧气的第一次长期积累开始于24亿年前（Ga），经典上被称为大氧化事件。尽管这一事件已经记录了一段时间，但越来越多的证据表明，氧气的动态趋势比以前认为的要多。有几条证据暗示此时的高含氧量，包括对氧化和还原反应敏感的元素的高现代浓度以及海洋页岩中的高有机碳。最近的研究表明，这些氧合趋势在约2.05 G后发生逆转，这与长期以来认为氧气随时间增加的观点相反。这个脱氧事件的解决很差，但可能提供重要的联系，以了解如何表面条件是不足以复杂的生物进化。它还可以提供海洋化学快速变化的类似物，让人想起现代气候变化的情况。目的：我的研究计划旨在揭示我们呼吸的空气的早期发展阶段。这项研究整合了先进的分析技术，解决了全球性的重大问题，包括地球初出茅庐的表面氧气条件的原因和后果。一个强有力的氧历史记录提供了深入了解生命的共同进化或阻碍它的因素。“鸡和蛋”的争论仍然存在于文献中，关于大气氧气上升的原因和影响，全球冰川和生物进化，包括含氧光合作用的出现。* 科学方法：过去的环境条件将使用补充地球化学方法，包括铀，铬和钼的同位素，加上氧化还原敏感元素的浓度重建。这项研究将使用这些工具跟踪早期的氧气条件，以阐明海洋沃茨缺氧条件的程度。地层学和放射性测年方法将有助于确定这些变化的速度和时间。影响力：地球系统经历了一次重大的扰动，使类似现代环境条件的趋势脱轨，但对这种逆转缺乏可能的机械解释。这项研究将调查有关的假设增加和减少氧气的趋势和浓度的生物可利用的元素在海洋中的关键时期在地质过去。将地球的路径拼凑到目前的含氧状态是解开地球系统中地球化学反馈的关键。过去海洋中的反馈机制有可能为现代缺氧沃茨的长期后果提供见解，这些海水随着现代气候变化而增加。 **

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. **