Determining the origin and evolutionary history of volatiles on Earth

由于表面覆盖着液态水，地球在太阳系的其他行星中脱颖而出，成为唯一已知的能够支持生命的避难所。但是，是什么让地球如此独特呢？它赖以生存的海洋和大气来自哪里？这些都是驱使我进行科学研究的基本问题。当45亿年前地球形成时，太阳系是一个非常不同的、混乱的地方。地球是由千米大小的小行星反复碰撞而成的。这些撞击将产生巨大的能量，这些能量将把海洋和大气喷射到太空中，使其干燥，缺乏生命所必需的成分。因此，地球是如何成为我们今天所知的富含挥发性物质的行星仍然是一个谜。要了解挥发性元素是如何到达地球的，我们需要从它们的组成中寻找线索，这些线索可以让我们找到它们的起源。然而，地球活跃的地质和生物已经抹去了可能存在于地球表面的任何潜在指纹。幸运的是，在地幔深处，有一些地区与地表隔离了数十亿年，仍然保留着解开地球挥发物神秘来源所需的信息。因此，我计划分析火山岩和从地球深处喷发的古代钻石中捕获的挥发物的组成。这项研究将为挥发物到达地球的方式和时间提供新的线索，并评估地质过程如何在地球历史上重新分配这些挥发物。更具体地说，它将解决关于地球挥发循环的三个核心问题1)地幔中的挥发性物质的来源是什么，以及地球是否从多个不同的来源获得挥发性物质？稀有气体是惰性挥发性元素，显示出不同吸积源(太阳、球粒陨石、彗星等)之间的可分辨同位素和元素差异。使它们成为了解地球上挥发物来源的关键工具。通过分析玄武岩玻璃中的稀有气体同位素，我将试图揭示地球地幔中挥发物的来源，并更好地了解地球挥发物到底起源于太阳系的什么地方。2)挥发物何时开始循环到地幔，以及俯冲过程如何随时间改变地幔的挥发性收支？地球表面的环境和气候受到大气层和地幔之间挥发性物质(如水、碳和氮)的运动的调节。挥发分进入地幔的主要过程是俯冲作用。这一过程是地球独有的，可能是防止影响我们邻近行星金星的失控温室气体条件的关键。然而，尽管挥发性俯冲在控制地球宜居性方面发挥了重要作用，但目前还不清楚挥发性物质何时开始返回地幔。在这个项目中，我将分析古代钻石中的挥发物，以寻找古代俯冲的迹象，并确定挥发物开始返回地幔的时间和程度。3)俯冲作用是否异质地将不同的挥发分循环到地幔中？从火山弧的物质平衡计算可知，至少有一些挥发物在俯冲过程中幸存下来，并进入地幔。然而，这些挥发物是如何在地幔中分布的还不太为人所知。通过将对卤素和氮的分析与具有容易识别的俯冲特征的重惰性气体相结合，我将确定地幔中的卤素和氮在多大程度上具有循环来源，并提供对控制它们在整个地幔中分布的地幔动力学的洞察。

With its surface covered in liquid water, the Earth stands out amongst the other planets of the solar system as the only known haven capable of supporting life. But what makes the Earth so unique? And where did its life-supporting oceans and atmosphere originate? These are the fundamental questions that drive my scientific research.When Earth formed 4.5 billion years ago, the solar system was a very different, chaotic, place. The Earth grew from repeated collisions between kilometre-sized asteroids. These impacts would have generated huge amounts of energy that would have ejected the oceans and atmosphere in to space, leaving it dry and barren of the ingredients essential for life. So how the Earth became the volatile-rich planet we know today remains a mystery.To understand how volatile elements arrived on Earth we need to looks for clues in their composition that could point us to their origin. However, the Earth's active geology and biology has wiped out any potential fingerprints that may have existed on the Earth's surface. Fortunately, deep inside the Earth's mantle there are regions that have remained isolated from the surface for billions of years, and still retain the information needed to solve the mysterious origin of Earth's volatiles. I therefore plan to analyse the composition of volatiles trapped in volcanic rocks and ancient diamonds erupted from deep within the Earth. This research will shed new light on, how and when, volatiles arrived on Earth, and evaluate how geological processes redistributed these volatiles throughout Earth's history. More specifically it will enable three central questions concerning the Earth's volatile cycle to be addressed 1) What is the origin of volatiles trapped within the mantle, and did Earth acquire volatiles from multiple different sources? Noble gases are inert volatile elements that show resolvable isotopic and elemental differences between different accretionary sources (solar, chondritic, cometary, etc.) making them key tools for understanding the origin of volatiles on Earth. By analysing noble gas isotopes within basaltic glasses I will attempt to reveal the origin of volatiles in Earth's mantle and provide a better understanding on the where exactly in the solar system did the Earth's volatiles originate.2) When did volatiles first started being recycled to the mantle, and how has the process of subduction modified the mantle volatile budget through time? The Earth's surface environment and climate is modulated by the movement of volatiles such as water, carbon and nitrogen between the atmosphere and the mantle. The main process through which volatiles are introduced to the mantle is through subduction. This process is unique to the Earth and may have been key in preventing the runaway greenhouse conditions that affected our neighbouring planet Venus. However despite the important role volatile subduction plays in controlling the habitability of the Earth it is not currently well understood when this return flux of volatiles to the mantle commenced. In this project I will analyse volatiles in ancient diamonds to search for signs of ancient subduction and determine when and to what extent volatiles started being returned to the mantle. 3) Does subduction heterogeneously recycle different volatiles in to the mantle? From mass balance calculations at volcanic arcs it is known that at least some volatiles survive the subduction process and make it in to the mantle. However, how these volatiles are then distributed throughout the mantle is less well known. By combining the analysis of halogens and nitrogen with the heavy noble gases, which have an easily identifiable subducted signature I will determine to what extent halogens and nitrogen in the mantle have a recycled origin, and provide an insight into the mantle dynamics that control their distribution throughout the mantle.