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

使地球成为一颗独特的行星的一个方面是富含氧气的大气层的存在。地质数据显示，这种情况已经持续了20多亿年。然而，在更深的时间，在地球最早的发展阶段，有证据表明，大气层与今天的大气层有很大的不同，稳定的自由氧基本上是不存在的，二氧化碳和甲烷是主要成分。实际上，地球的大气层与金星和火星的大气层成分更相似。人们普遍认为，能够进行光合作用的细菌有机体的进化使地球免于与姐妹行星分享命运。尽管这一观点看起来很聪明，但过去20年来积累的地质证据表明，这一观点过于简单化，很可能是错误的。研究时间的关键时刻被称为太古代-元古代过渡，大约25亿至20亿年前。这是地球历史上属于这一时期的岩石，是存在大量游离氧的第一个地质证据。然而，在数亿年前的岩石中发现了古代产氧光合作用的有机分子。因此，改变地球氧化状态的不仅仅是生物学，而是一些因素的组合，这些因素不仅影响氧气的产生速度，还影响氧气的消耗速度。因此，除了生命本身的存在，大气中氧气的增加，地球上最重要的进化方面的“如何”和“何时”还不清楚。一个独特的机会现在出现在我们面前。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--芬诺斯堪地盾俄罗斯部分--中回收了总共3.6公里的原始岩心。该项目被称为FAR-DEEP（Fennoscandian Arctic Russia - Drilling Early Earth Project），代表了国际合作努力，以寻找这些深层科学问题的答案，并获得了国际大陆钻探计划和相关资助合作伙伴，德国，挪威，美国和NASA的国家资助机构的150万美元。岩芯现存放在挪威地质调查局，第二阶段的研究即将开始，即岩芯的定性、分析和解释。我们有一套综合的专业知识，以贡献基础知识，这是FAR-DEEP科学目标的核心;该目标是开发一个全面的理解和自洽的模型，解释自由氧如何在地球上变得丰富，从而为现代有氧地球系统的出现奠定了基础。我们将利用英国的两个顶级分析设施，苏格兰大学环境研究中心和NERC同位素地球科学实验室，以获得高分辨率的地球化学数据和高精度的地质年代学，这些数据将被链接到一个完整的记录和约束的地质框架（综合核心和露头数据集）。本提案中概述的研究的成功和获得的数据将支持FAR-DEEP项目的所有后续分析和推断，从而确保实现其目标。

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.