Response of the Nitrogen Cycle to Ocean Redox Chemistry During the Great Oxidation Event

推动自然科学的最基本的问题之一是地球上的生命是如何进化的。了解这颗行星上的生命是如何进化的，也有助于我们在其他太阳系寻找宜居行星。我们现在确定无疑的是，简单的单细胞生物是在30亿年前在海洋中进化出来的。我们还知道，自第一次细胞分裂以来，地球表面(大气和海洋)的化学成分发生了戏剧性的变化。然后我们试图理解的是，生命的进化如何响应并在某些情况下驱动了地球表面化学的这些变化。了解过去生命对地球上的地球化学变化的反应将有助于我们更清楚地预测未来生命将如何对化学变化做出反应，例如与快速逼近的气候变化相关的变化。影响海洋生命的主要参数之一是溶解氧的可用性，它不仅对所有高等生命形式的存在至关重要，而且直接控制构成生命基石的基本元素的分布和丰富程度。在地球历史的最初约35亿年里，海洋的特点是缺乏溶解氧，这种情况被称为缺氧。氧在大约24亿到23亿年前开始在大气和海洋中积聚，这可能是地球表面化学史上最戏剧性的事件，被称为大氧化事件。直到约5.8亿年前，大气中的氧气水平才上升到足以使海洋完全充氧的地步。在其间约20亿年的时间里，海洋的化学成分在不同的氧合水平之间迅速波动。因此，最近科学研究的一个主要焦点是识别和了解生物学的反应以及必需营养物质对环境中不同数量的氧气的循环。氮是所有生物的基本元素，与碳和磷一起是蛋白质、氨基酸、DNA和RNA形成所必需的。氮在生物圈中的分布由生物反应控制，这些反应对环境参数做出反应，包括可用氧气量。尽管氮对生命很重要，但人们对氮循环如何响应地球历史上氧气浓度的波动知之甚少。该项目的目的是专门解释全球氮循环对大氧化事件期间大气和海洋含氧量变化的反应。这将通过对现代氮循环中重要的微生物进行实验室实验，并将实验研究结果应用于研究跨越大氧化事件的沉积岩中的氮和氧化指示物来实现。

One of the most fundamental questions that drives natural sciences is how life evolved on Earth. Understanding how life evolved on this planet also informs our search for habitable planets in other solar systems. What we now know beyond a reasonable doubt is that simple single-celled organisms evolved in the ocean greater than 3 billion years ago. We also know that the chemistry of the Earth's surface (both the atmosphere and the oceans) has undergone dramatic changes since that first cell division occurred. What we then seek to understand is how the evolution of life has responded to, and in some cases driven, these changes in Earth surface chemistry. Understanding how life responded to geochemical changes on the planet in the past will additionally help us to more clearly predict how life will respond to chemical changes in the future, for example associated with rapidly approaching climate change. One of the major parameters that affects life in the ocean is the availability of dissolved oxygen, which is not only essential for all higher life forms to exist, but also directly controls the distribution and abundance of essential elements that make up the building blocks of life. For the first ~3.5 billion years of Earth history, the ocean was characterized by a lack of dissolved oxygen, a situation known as anoxia. Oxygen first began to build up in the atmosphere and oceans between ~2.4 and 2.3 billion years ago, in perhaps the most dramatic event in the history of Earth surface chemistry, termed the Great Oxidation Event. It was not until ~580 million years ago that oxygen levels in the atmosphere rose sufficiently to completely oxygenate the oceans. In the intervening ~2 billion years, the chemistry of the oceans fluctuated rapidly between various levels of oxygenation. Thus a major focus for scientific research recently has been on identifying and understanding the response of biology and the cycling of essential nutrients to variable amounts of oxygen in the environment. Nitrogen is an essential element in all living organisms, required along with carbon and phosphorus for the formation of proteins, amino acids, DNA and RNA. The distribution of nitrogen in the biosphere is controlled by biological reactions that respond to environmental parameters, including the amount of available oxygen. Despite the importance of nitrogen to life, very little is known about how the nitrogen cycle responded to fluctuations in oxygen concentrations over Earth history. The aim of this project is specifically to interpret the response of the global nitrogen cycle to changes in the oxygen content of the atmosphere and oceans during the Great Oxidation Event. This will be accomplished by laboratory experiments with microorganisms that are important in the modern nitrogen cycle, and application of the results of the experimental studies to the investigation of nitrogen and indicators of oxygenation in sedimentary rocks spanning the Great Oxidation Event.