Did biogeochemical methane cycling regulate the Neoarchean atmosphere?

数十亿年前，年轻的地球与我们今天居住的地球大不相同，温度剧烈波动，大气层充满有毒气体。了解我们是如何从那个荒凉的地方发展到今天的世界，以温和的气候和大型氧基生命形式为主，是地球科学的一个基本问题。一个重要的转变发生在大约25亿年前（Ga），称为大氧化事件（GOE），当时地球大气中的氧气浓度首次从接近零增加到现代水平的一小部分。自然科学研究的一个主要焦点是确定地球系统（包括生命）如何在环境中产生如此巨大的变化;然而，GOE究竟是如何以及为什么发生的仍然是一个谜。要理解早期地球向含氧环境的过渡，不可或缺的是对古代大气成分的定量估计。使用大多数地球化学工具很难做出这些估计，因为这些工具往往反映的是海洋环境中发生的过程。这项研究建议将直接反映大气中发生的化学反应的硫的四种稳定同位素与将这些地球化学特征与大气成分联系起来的数值模型联系起来。另外一套地球化学分析将使我们能够确定海洋的化学性质以及生物圈在同一时间的作用方式。这项研究的独特之处在于它结合了这些多种技术，我们将应用于GOE之前沉积的保存完好的沉积物，以确定地球大气在此期间如何发展，以及海洋和生物圈如何做出贡献和反应。了解大气，海洋和生命之间的相互作用是特别重要的，在这段时间内，因为它代表了一个地球系统在全球表面chemical.We的一个重大转变的边缘，我们已经进行了一个初步的类似的分析~2.65-2.5 Ga沉积物，描绘了一个不寻常的地球环境的一个诱人的图片GOE之前。这些分析指出，大气层不仅氧气含量非常低，而且还周期性地由高甲烷水平产生的有机颗粒层（称为“薄雾”）所主导，类似于土星的卫星泰坦。我们将扩展从这些初步分析中发展出来的假设，并探讨它们对地球表面化学发展和地球历史上这一关键时期生命进化的意义。

Billions of years ago the young planet Earth was much different from the one we inhabit today, with wildly fluctuating temperatures and an atmosphere filled with toxic gases. Understanding how we got from that inhospitable place to the world of today, dominated by mild climates and large oxygen-based life forms, is a fundamental question in Earth sciences. One important transition occurred approximately 2.5 billion years ago (Ga), called the Great Oxidation Event (GOE), when the oxygen concentrations in Earth's atmosphere first increased from near zero to a fraction of modern levels. A major focus of research in natural science is determining how the Earth system (including life) has acted to produce such monumental changes in the environment; however, exactly how and why the GOE occurred remains a mystery. Integral to understanding the transition to an oxygenated environment on the early Earth are quantitative estimates of the composition of the ancient atmosphere. These estimates are difficult to make using most geochemical tools, which tend to reflect processes that occurred in the marine environment instead. This study proposes to link the four stable isotopes of sulfur, which directly reflect chemical reactions that occurred in the atmosphere, with numerical models tying these geochemical signatures to atmospheric compositions. An additional set of geochemical analyses will allow us to determine the chemistry of the oceans and how the biosphere was acting at the same time. This study is unique in its combination of these multiple techniques, which we will apply to well-preserved sediments deposited directly before the GOE, to determine how the Earth's atmosphere developed during this time, and how the oceans and biosphere both contributed and responded. Understanding the interactions between the atmosphere, oceans, and life is particularly crucial during this time period, as it represents an Earth system poised at the edge of a major transition in global surface chemistry.We have performed a preliminary set of similar analyses on ~2.65-2.5 Ga sediments that paint a tantalizing picture of an unusual Earth environment directly before the GOE. These analyses point to an atmosphere that was not only very low in oxygen, but was also periodically dominated by a layer of organic particles (termed "haze") produced at high methane levels, similar to that seen on Saturn's moon Titan. We will expand upon the hypotheses developed from these preliminary analyses and explore their significance for the development of Earth surface chemistry and the evolution of life during this critical period in Earth history.