Evolution of the nitrogen cycle and the rise of oxygen

氮循环的演变和氧气的增加

• 批准号: 0844252
• 负责人: Linda Godfrey
• 金额: $ 10万
• 依托单位: Rutgers University New Brunswick
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-15 至 2010-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0844252&HistoricalAwards=false
• 关键词: Evolution; nitrogen; cycle; rise; oxygen

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The atmosphere of the Earth is dominated by two gases, N2 and O2. N2 is virtually inert and has been the most abundant gas since the atmosphere formed. In contrast, O2, which came to comprise 10 to 30% of the volume of the atmosphere over the past ~500 million years, is highly reactive and must be produced continuously by the photobiological oxidation of water. The cycles of these two elements are linked; the fluxes of N are entirely controlled by biological reactions that are strongly influenced by the concentration of oxygen in the environment. The major goal of the proposed research is to elucidate the interactions and feedbacks between the cycles of nitrogen and oxygen from the middle Archean to middle Proterozoic, a period in Earth?s history when it permanently ?tipped? from being an anaerobic or microaerobic planet, to one with an atmosphere sufficiently rich in oxygen to permit the formation of a stratospheric ozone layer.The proposed research is based on an understanding of the N isotope composition of sedimentary organic matter, which can be used to characterize the dominant form of N that was assimilated by autotrophic organisms. Specifically, we propose to use the isotope fractionations associated with the successive transfers of N through the O-dependent N-cycle to determine the paleoredox state of the Precambrian ocean, and its correlatation with inferred geological events. We focus on three sample sets: 1) the Mesoarchean to early Proterozoic in South Africa; 2) late Paleoproterozoic in the Animikie Basin and 3) Meosproterozoic Roper Gp. We will also investigate other samples from North America in order to fill temporal gaps between these three samples sets, or to provide spatial coverage and diversity of environments at specific times.Our approach utilizes careful, high precision, analytical techniques combined with a simple, elegant box model of the coupled CNO cycles with an embedded N isotope submodel. All ä15N analyses in the reported in the literature for Precambrian sediments have very high C/N ratios, indicative of N loss, but little attention is given to changes in ä15N that may have resulted. We will analyze N and N isotopes in bulk material, kerogen, and in fixed lattice sites to determine whether the N isotope system is closed. In collaboration with colleagues at JAMSTEC, a subset of samples will be analyzed for porphyrin ä15N. We will also analyze selected samples for phyllosilicate mineralogy and major element chemistry to address possible N leaching by potassic or saline fluids which can affect ä15N. Finally, we will build upon our earlier modeling efforts to develop a model that will use N isotopes in a fully integrated model of the N, O, C, S and Fe cycles as the oxidation state of Earth?s surface increased during the Precambrian.Broader ImpactsThe results of this proposed work will be significant to increasing our understanding how the N and O cycles interacted early in Earth?s history. We can use the changes in ä15N of organic matter, in conjunction with other isotope records and from modeling work to determine the progression from a fully anoxic ocean to oxic surface/anoxic deep to a fully oxic ocean state corresponding to nitrate dominance of the fixed N pool.We have developed an outreach program to improve ocean science literacy. However our research is also intended to assist educators who are in the center of debates regarding creationism and intelligent design, with little guidance on evolution. IMCS and Geology run open houses where this research will be highlighted, and it will be part of a summer workshop as part of ESTEEM, a Rutgers-NJ Dept of Education initiative directed at middle schools. This project will provide an undergraduate student with the opportunity to participate in a collaborative study involving different universities and countries. The students will be involved in laboratory work and will have the opportunity to work with professors, researchers, and students at Rutgers and Lehigh Universities, and encouraged to present their work at meetings.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。地球的大气层主要由两种气体N2和O2组成。氮气实际上是惰性的，自大气形成以来一直是最丰富的气体。相比之下，在过去约5亿年里占大气体积10%至30%的O2是高活性的，必须通过水的光生物氧化不断产生。这两个元素的循环是联系在一起的；氮的通量完全由受环境中氧浓度强烈影响的生物反应控制。本研究的主要目的是阐明中太古宙至中元古代（地球上的一个时期）氮氧循环之间的相互作用和反馈。美国历史何时永久倾斜？从一个无氧或微氧行星，到一个有足够丰富的氧气的大气层，允许平流层臭氧层的形成。提出的研究是基于对沉积有机质氮同位素组成的理解，这可以用来表征被自养生物同化的氮的主要形式。具体而言，我们建议使用与N通过o依赖的N循环的连续转移相关的同位素分馏来确定前寒武纪海洋的古氧化还原状态及其与推断的地质事件的相关性。我们重点研究了三个样品集：1)南非的中太古代至早元古代；2) Animikie盆地晚古元古代和3)中元古代Roper Gp。我们还将调查来自北美的其他样本，以填补这三个样本集之间的时间空白，或提供特定时间环境的空间覆盖和多样性。我们的方法利用细致、高精度的分析技术，结合了简单、优雅的CNO耦合循环盒模型和嵌入的N同位素子模型。文献中报道的所有ä15N对前寒武纪沉积物的分析都有非常高的C/N比率，表明N损失，但很少注意到ä15N可能导致的变化。我们将分析大块材料、干酪根和固定晶格位点中的N和N同位素，以确定N同位素系统是否封闭。与JAMSTEC的同事合作，将分析一部分样品中的卟啉ä15N。我们还将分析选定样品的层状硅酸盐矿物学和主要元素化学，以解决钾或盐水可能影响ä15N的N浸出。最后，我们将在早期建模工作的基础上开发一个模型，该模型将使用N同位素作为地球氧化态的N， O， C， S和Fe循环的完全集成模型。地球表面在前寒武纪有所增加。更广泛的影响这项拟议工作的结果将对增加我们对地球早期N和O循环如何相互作用的理解具有重要意义。年代的历史。我们可以利用ä15N的有机物变化，结合其他同位素记录和建模工作来确定从完全缺氧海洋到缺氧表面/缺氧深层到完全缺氧海洋状态的过程，对应于固定N池的硝酸盐优势。我们制定了一个推广计划来提高海洋科学素养。然而，我们的研究也旨在帮助那些处于关于神创论和智能设计争论中心的教育工作者，他们在进化论方面缺乏指导。IMCS和地质学将举办开放日活动，重点介绍这项研究，这将是一个夏季研讨会的一部分，作为ESTEEM的一部分，ESTEEM是罗格斯大学-新泽西州教育部针对中学的倡议。该项目将为本科生提供参与不同大学和国家合作研究的机会。学生将参与实验室工作，并有机会与罗格斯大学和里海大学的教授、研究人员和学生一起工作，并鼓励他们在会议上展示自己的工作成果。