Evolution of the nitrogen cycle and the rise of oxygen

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组成，氮气和氧气。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，氧气在过去的5亿年里占大气体积的10%到30%，是高度活性的，必须通过水的光生物氧化不断产生。这两种元素的循环是相连的；氮的通量完全由生物反应控制，这些反应受到环境中氧气浓度的强烈影响。这项研究的主要目的是阐明中太古代至中元古代之间氮氧循环之间的相互作用和反馈，这是地球历史上S永久倾倒的时期。从厌氧行星或微氧行星，到大气中氧气充足，足以形成平流层臭氧层的行星。拟议的研究是基于对沉积有机质的N同位素组成的理解，这可以用来表征被自养生物同化的N的主要形式。具体地说，我们建议使用与N通过依赖氧的N旋回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。我们重点研究了三组样品：1)南非的中太古代-早元古代；2)阿尼基盆地的晚古元古代；3)中元古代的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差距，或提供特定时间的空间覆盖和环境多样性。我们的方法利用仔细、高精度的分析技术，结合简单、优雅的耦合CNO旋回盒子模型和嵌入的N同位素子模型。文献中报道的前寒武纪沉积物的所有ä15N分析都有很高的C/N比，表明N的损失，但很少有人注意到可能导致的ä15N的变化。我们将分析块状物质、干酪根和固定晶格位置中的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，将对部分样本进行卟啉ä15N分析。我们还将对选定的样品进行层状硅酸盐矿物学和主要元素化学分析，以解决钾盐或盐水可能会影响ä15N的氮淋滤问题。最后，我们将在以前的模拟工作的基础上开发一个模型，该模型将使用N同位素在N、O、C、S和铁旋回的完全集成的模型中，随着地球？S在前寒武纪期间表面氧化状态的增加。广泛的影响这项拟议的工作的结果将对增加我们对地球？S历史早期N和O旋回如何相互作用的理解具有重要意义。我们可以结合其他同位素记录和模拟工作，利用有机质在ä15N中的变化来确定从完全缺氧的海洋到缺氧的表面/缺氧的深处，再到与固定N池的硝酸盐优势相对应的完全氧化的海洋状态。我们制定了一个推广计划，以提高海洋科学素养。然而，我们的研究也是为了帮助那些处于创世论和智能设计争论中心的教育者，他们几乎没有关于进化论的指导。IMCS和地质学举办了开放日，这项研究将在那里得到强调，这将是罗格斯-新泽西州教育部针对中学的一项倡议--尊重--夏季研讨会的一部分。该项目将为本科生提供参与涉及不同大学和国家的合作研究的机会。这些学生将参与实验室工作，并将有机会与罗格斯大学和利哈伊大学的教授、研究人员和学生合作，并鼓励他们在会议上展示他们的工作。

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.