Critical new perspectives on molybdenum cycling under modern and experimental euxinic conditions: Tuning the paleoredox proxy

现代和实验性环境条件下钼循环的重要新观点：调整古氧化还原代理

• 批准号: 1124327
• 负责人: Timothy Lyons
• 金额: $ 29.85万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-10-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1124327&HistoricalAwards=false
• 关键词: Critical; new; perspectives; molybdenum; cycling

The story of ancient ocean chemistry is the story of our origins. The geologic record reveals the presence of animals over only the last 10% of Earth?s 4.6-billion-year history and the origins of modern humans only a flicker of time ago. Most researchers link the appearance of the first animals to a rise in atmospheric oxygen to a level high enough to support complex animal metabolisms. The first 90% of Earth history, however, is a story of profound change in the oxygen state of the atmosphere and ocean, with complete absence of oxygen over the first half of Earth history and an oxygen-free deep ocean for most of the next half. Oxygen abounds today, and the ocean teems with animals, yet the oxygen-lean landscape of the early ocean was the cradle of our ancestors. The best view of these early organisms and their surroundings comes from fossils and the chemical properties of sediments deposited within the ancient ocean, and no element in the periodic table has played a greater role than molybdenum (Mo) as a window to the past.Molybdenum, a nutrient essential in the biological cycling of nitrogen, must have been a determining factor in the paths and rates that led ultimately to the early evolution of marine animals, particularly since its concentration in seawater varies dramatically with the availability of oxygen. This and other life-sustaining metals can be scrubbed out of seawater in the presence of hydrogen sulfide, which probably spread through sizeable portions of the ancient ocean. Recent research by this group and a few others has come a long way in providing a roadmap to the chemistry of ancient seawater based on the distributions and isotopic properties of Mo in ancient sediments, but key questions remain. Our understanding of the co-evolution of early life and ocean chemistry can only be as strong as the knowledge of how Mo is cycled now and in the past?particularly under the oxygen-poor conditions that dominated the early ocean. This study seeks to use novel, cutting-edge analytical methods in the lab and in the field to fill essential gaps in our grasp of Mo biogeochemistry. Among the key issues and questions are the mechanisms of Mo uptake across diverse depositional settings, particularly those with abundant hydrogen sulfide in the seawater. What specifically are the relationships to organic matter, the remains of organisms, and are the isotopes of Mo fractionated during interactions with organic substrates? Isotopes are atoms of the same element that differ in their masses and specific reaction behaviors and so can provide unique information about chemical pathways and the controlling environmental factors, such as oxygen availability. What is the full range of potential Mo hosts in settings rich in hydrogen sulfide, and how does dissolved Mo speciate and fractionate isotopically under those conditions? Although these chemical questions are quite specific, the implications are broad and speak to the ability to fingerprint conditions in the ocean that either fostered or challenged the origins and diversification of early life. The impact of this study will extend widely. A far greater ability to unravel the history of life is an expected outcome, and investigators will develop and refine novel analytical methods with broader relevance to many other trace metals and their biogeochemical cycles, including those in the modern ocean. Thanks to their hard-earned experience they are now able to demonstrate the great utility of particle accelerators in geobiological research. They aim to smooth the path for others traveling the same route by providing a virtual experience (website and short course) that captures their analytical maturation from beginners to experts, spanning from the particulars of our experience to more general logistical and scientific details (a sort of ?Synchrotron for Dummies?). They plan a high level of undergraduate involvement that mirrors UCR?s status as one of the most culturally diverse campuses in America. Finally, in an effort to reach across international boundaries, investigators have planned monthly group meetings with their colleagues in Beijing designed to emphasize student presentations, to enhance the flow of ideas in both directions, and to foster additional collaborative exploration of the early ocean and its co-evolving life. Although the methods are diverse and demanding, their motivations distill down to a single simple question: where did we come from?

古代海洋化学的故事就是我们起源的故事。地质记录揭示了地球 46 亿年历史的最后 10% 中仅存在动物，而现代人类的起源也只是在不久之前。大多数研究人员将第一批动物的出现与大气中氧气含量上升到足以支持复杂的动物新陈代谢的水平联系起来。然而，地球历史的前 90% 是大气和海洋中氧气状态发生深刻变化的故事，地球历史的前半段完全没有氧气，而接下来的大部分时间都是无氧的深海。一半。如今氧气充足，海洋里充满了动物，但早期海洋的贫氧景观却是我们祖先的摇篮。对这些早期生物及其周围环境的最佳观察来自化石和远古海洋中沉积物的化学性质，元素周期表中没有任何元素比钼 (Mo) 发挥了更大的作用，它作为了解过去的窗口。钼氮是氮生物循环中必需的营养物质，它一定是最终导致海洋动物早期进化的路径和速度的决定性因素，特别是因为它在海水中的浓度随着氧气的供应而发生巨大变化。这种金属和其他维持生命的金属可以在硫化氢存在的情况下从海水中洗掉，硫化氢可能扩散到古代海洋的相当大的部分。该小组和其他一些人的最新研究在根据古代沉积物中钼的分布和同位素性质为古代海水化学提供路线图方面取得了长足的进步，但关键问题仍然存在。我们对早期生命和海洋化学共同进化的理解只能与对现在和过去钼如何循环的了解一样深入——特别是在早期海洋占主导地位的缺氧条件下。本研究旨在在实验室和现场使​​用新颖、前沿的分析方法来填补我们对钼生物地球化学掌握的重要空白。关键问题包括不同沉积环境中钼的吸收机制，特别是海水中富含硫化氢的沉积环境。与有机物、生物体残骸的具体关系是什么？钼同位素在与有机底物相互作用过程中是否发生了分馏？同位素是相同元素的原子，其质量和特定反应行为不同，因此可以提供有关化学途径和控制环境因素（例如氧气可用性）的独特信息。在富含硫化氢的环境中，潜在的钼主体的全部范围是什么？溶解的钼在这些条件下如何形成和同位素分馏？尽管这些化学问题非常具体，但其影响是广泛的，并且涉及对海洋中促进或挑战早期生命的起源和多样化的条件进行指纹识别的能力。这项研究的影响将广泛延伸。预期的结果是解开生命历史的能力大大提高，研究人员将开发和完善与许多其他痕量金属及其生物地球化学循环（包括现代海洋中的生物地球化学循环）更广泛相关的新颖分析方法。凭借他们来之不易的经验，他们现在能够展示粒子加速器在地球生物学研究中的巨大效用。他们的目标是通过提供虚拟体验（网站和短期课程）来为其他走同样路线的人铺平道路，捕捉他们从初学者到专家的分析成熟度，从我们的经验细节到更一般的后勤和科学细节（一种的《同步加速器傻瓜书》）。他们计划提高本科生的参与度，这反映了加州大学河滨分校作为美国文化最多元化的校园之一的地位。最后，为了跨越国际边界，研究人员计划每月与北京的同事举行小组会议，旨在强调学生的演讲，加强双向思想交流，并促进对早期海洋及其周边地区的进一步合作探索。共同进化的生命。尽管方法多种多样且要求很高，但它们的动机可归结为一个简单的问题：我们从哪里来？