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。地质记录显示动物只在地球最后10%的地方存在？中国有46亿年的历史，而现代人类的起源只是一瞬间。大多数研究人员将第一批动物的出现与大气中氧气的上升联系起来，氧气的水平高到足以支持复杂的动物代谢。然而，地球历史的前90%是大气和海洋氧气状态发生深刻变化的故事，在地球历史的前半部分完全没有氧气，而在下半部分的大部分时间里都是无氧深海。今天氧气充足，海洋中充满了动物，但早期海洋的贫氧景观是我们祖先的摇篮。对这些早期生物及其周围环境的最佳看法来自化石和沉积在古海洋中的沉积物的化学性质，在周期表中没有任何元素比钼（Mo）作为过去的窗口发挥更大的作用。钼，氮的生物循环中必不可少的营养素，一定是最终导致海洋动物早期进化的路径和速率的决定性因素，特别是因为它在海水中的浓度随着氧气的可用性而发生巨大变化。在硫化氢存在的情况下，这种金属和其他维持生命的金属可以从海水中洗掉，硫化氢可能在古代海洋的相当大的部分中传播。该小组和其他一些人最近的研究已经取得了很大进展，根据古代沉积物中钼的分布和同位素特性，为古代海水的化学提供了路线图，但关键问题仍然存在。我们对早期生命和海洋化学的共同进化的理解，只能像对钼在现在和过去如何循环的知识一样强。特别是在早期海洋中缺氧的条件下。这项研究旨在在实验室和现场使用新的，尖端的分析方法，以填补我们掌握钼地球化学的重要空白。其中的关键问题和问题是跨不同的沉积环境，特别是那些在海水中含有丰富的硫化氢的钼吸收的机制。与有机质、生物体遗骸的关系是什么？钼的同位素在与有机基质相互作用的过程中是否发生分馏？同位素是同一元素的原子，它们的质量和特定的反应行为不同，因此可以提供有关化学途径和控制环境因素（如氧气可用性）的独特信息。在富含硫化氢的环境中，潜在的钼宿主的全部范围是什么？在这些条件下，溶解的钼是如何形成和分解的？尽管这些化学问题非常具体，但其影响是广泛的，并说明了海洋中的指纹条件的能力，这些条件要么促进要么挑战早期生命的起源和多样化。这项研究的影响将是广泛的。一个更大的能力来解开生命的历史是一个预期的结果，研究人员将开发和完善新的分析方法与更广泛的相关性，许多其他痕量金属及其地球化学循环，包括那些在现代海洋。由于他们来之不易的经验，他们现在能够证明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一种虚拟体验（网站和短期课程）来为其他同行者铺平道路，这种体验可以捕捉他们从初学者到专家的分析成熟度，从我们经验的细节到更一般的后勤和科学细节（一种？同步加速器的傻瓜？）。他们计划高水平的本科生参与，反映UCR？作为美国最具文化多样性的校园之一。最后，为了跨越国际界限，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，加强双向的思想交流，并促进对早期海洋及其共同进化生命的进一步合作探索。尽管这些方法多种多样，要求也很高，但它们的动机可以归结为一个简单的问题：我们从哪里来？