The Archaean-Proterozoic Transition: Constraining the Emergence of the Aerobic Earth System

地球作为一颗行星的一个独特之处在于其富含氧气的大气的存在。地质数据显示，这种情况已经持续了20多亿年。然而，在时间更深的时候，在地球最早的发展阶段，有证据表明，大气与今天的大气有很大不同，基本上没有稳定的游离氧，二氧化碳和甲烷是主要成分。实际上，地球上的大气层与金星和火星的大气成分更相似。普遍的观点是，能够进行氧气光合作用的细菌生物的进化拯救了地球，使其免于与其姊妹行星分享命运。尽管这种观点看似明智，但在过去20年里，越来越多的地质证据表明，这种观点过于简单化，而且很可能是错误的。需要研究的关键时刻是大约25亿到20亿年前的太古宙-元古界的过渡。正是来自属于地球历史上这一时期的岩石，才有了第一个证明自由氧水平显著的地质证据。然而，在数亿年前的岩石中发现了可归因于古代产氧光合作用的化石有机分子。因此，不仅仅是生物学改变了地球的氧化状态，而是一些因素的组合不仅影响了氧气的产生速度，也影响了氧气的消耗速度。因此，除了生命本身的存在和大气中氧气的上升之外，地球上最具进化意义的最深刻的方面是如何以及何时的，都是未知的。一个独特的机会现在呈现在我们面前。一个千载难逢的研究项目的第一阶段于2007年夏末完成--从地球上最好的太古代-古元古代岩石档案之一中发现了总共3.6公里的原始钻芯，这些岩石位于芬诺斯坎迪亚地盾的俄罗斯部分。该项目被称为远深(Fennoscandian北极俄罗斯-钻探早期地球项目)，代表着寻找这些深层科学问题答案的国际合作努力，并从国际大陆钻探计划和相关资金合作伙伴、德国、挪威、美国和美国国家航空航天局的国家资助机构获得了150万美元。这些岩心现在存放在挪威地质调查局，第二阶段的研究即将开始，即岩心的表征、分析和解释。我们拥有一套综合的专业知识，可以提供处于遥远深度科学目标核心的基础知识；该目标是开发一个全面理解和自洽的模型，解释地球上自由氧是如何变得丰富的，从而为现代地球有氧系统的出现奠定基础。我们将利用英国两个顶尖的分析设施，苏格兰大学环境研究中心和NERC同位素地球科学实验室，获得高分辨率的地球化学数据和高精度的地质年代学，这些数据将被连接到一个全面记录和受限的地质框架中(综合的岩心和露头数据集)。本提案中概述的研究的成功和所获得的数据将支持对深海项目的所有后续分析和推论，从而确保实现其目标。

Summary One aspect that makes Earth unique as a planet is the presence of an oxygen-rich atmosphere. Geological data reveal that this has been the case for more than two billion years. However, deeper in time, during Earth's earliest developmental phases, evidence exists that the atmosphere was much different than that of today's, stable free oxygen was essentially absent and carbon dioxide and methane were dominant components. In effect, Earth would have had an atmosphere more similar to the compositions of those of Venus and Mars. The widely held view is that the evolution of bacterial organisms capable of oxygenic photosynthesis saved Earth from sharing the fate of her sister planets. As intellectually elegant as that view seemingly is, geological evidence has been accumulating over the past two decades that indicates it is oversimplified and likely wrong. The critical juncture in time to examine is known as the Archean-Proterozoic transition, some 2.5 to 2.0 billion years ago. It is from rocks belonging to this period in Earth history that the first geological evidence exists for significant levels of free oxygen. However, fossilised organic molecules attributable to ancient oxygenic photosynthesisers are found in rocks hundreds of millions of years older. Thus, it was not biology alone that changed the oxidation state of Earth, but rather some combination of factors influencing not only the rate of oxygen production but also the rate of oxygen consumption. Consequently, the 'how' and the 'when' of the singlemost, evolutionarily profound aspect of Earth, other than the presence of life itself, the rise of atmospheric oxygen, are not known. A unique opportunity has now presented itself to us. The first phase of a once-in-a-career research project was completed late in the summer of 2007 - a total of 3.6 km of pristine drill cores was recovered from one of the finest archives of Archean-Palaeoproterozoic rocks on Earth, those in the Russian portion of the Fennoscandian Shield. This project, known as FAR-DEEP (Fennoscandian Arctic Russia - Drilling Early Earth Project), represents an international collaborative effort to find answers to these deep scientific questions and was awarded $1.5M from the International Continental Drilling Program and associated funding partners, the national funding institutions of Germany, Norway, the USA and NASA. The cores are now housed at the Norwegian Geological Survey and the second phase of research is about to begin, the characterization, analyses and interpretation of the cores. We have a combined suite of expertise to contribute fundamental knowledge that lies at the heart of the scientific goal of FAR-DEEP; that goal is to develop a comprehensive understanding and self-consistent model explaining how free oxygen became abundant on Earth and thereby laid the foundations for the emergence of the modern aerobic Earth System. We will utilise two of the UK's top analytical facilities, the Scottish Universities Environmental Research Centre and the NERC Isotope Geoscience Laboratory, to obtain high-resolution geochemical data and high-precision geochronology that will be linked into a thoroughly documented and constrained geological framework (integrated core and outcrop datasets). The success of the research outlined in this proposal and the data obtained will underpin all subsequent analyses and inferences of the FAR-DEEP project and thereby assure that its goal is realised.