Determining the origin and evolutionary history of volatiles on Earth

确定地球上挥发物的起源和进化历史

• 批准号: NE/X01732X/1
• 负责人: Michael Ward Broadley
• 金额: $ 99.41万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX01732X%2F1
• 关键词: Determining; origin; evolutionary; history; volatiles

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.

由于其表面覆盖着液态水，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风港。但是什么让地球如此独特呢？其维持生命的海洋和大气起源于哪里？这些是推动我科学研究的基本问题。45 亿年前地球形成时，太阳系是一个非常不同、混乱的地方。地球是由公里大小的小行星之间的反复碰撞而形成的。这些撞击会产生大量能量，将海洋和大气喷射到太空中，使太空干燥且缺乏生命必需的成分。因此，地球如何成为我们今天所知道的富含挥发物的星球仍然是一个谜。为了了解挥发性元素是如何到达地球的，我们需要寻找其成分的线索，这些线索可以为我们指明它们的起源。然而，地球活跃的地质和生物学已经消除了地球表面可能存在的任何潜在指纹。幸运的是，在地幔深处，有一些区域数十亿年来一直与地表隔绝，并且仍然保留着解决地球挥发物神秘起源所需的信息。因此，我计划分析火山岩和从地球深处喷发的古代钻石中的挥发物的成分。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整个地球历史中重新分配这些挥发物。更具体地说，它将能够解决有关地球挥发物循环的三个核心问题：1）困在地幔中的挥发物的来源是什么，地球是否从多个不同来源获得了挥发物？稀有气体是惰性挥发性元素，在不同的增生源（太阳、球粒陨石、彗星等）之间表现出可解析的同位素和元素差异，使其成为了解地球上挥发物起源的关键工具。通过分析玄武岩玻璃中的稀有气体同位素，我将尝试揭示地幔中挥发物的起源，并更好地了解地球挥发物在太阳系中的确切起源。2）挥发物何时开始被再循环到地幔，俯冲过程如何随时间改变地幔挥发物预算？地球表面环境和气候受到水、碳和氮等挥发物在大气和地幔之间的运动的调节。将挥发物引入地幔的主要过程是通过俯冲。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条件的关键。然而，尽管挥发物俯冲在控制地球宜居性方面发挥着重要作用，但目前尚不清楚挥发物何时开始返回地幔。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，并确定挥发物何时以及在多大程度上开始返回地幔。 3）俯冲作用是否会异质地将不同的挥发物再循环到地幔中？根据火山弧的质量平衡计算可知，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，这些挥发物如何分布在整个地幔中却鲜为人知。通过将卤素和氮与具有易于识别的俯冲特征的重惰性气体的分析相结合，我将确定地幔中的卤素和氮在多大程度上具有循环来源，并深入了解控制其在整个地幔中分布的地幔动力学。