The oxygen fugacity of core segregation and the redox evolution of the mantle: constraints from iron and chromium isotopes

我们对地球的起源知之甚少，它是如何随时间演变的，以及它是如何适合生命的。围绕气候变化、寻找太阳以外的恒星周围的新行星以及前往我们太阳系内的行星的任务等问题存在着相当大的争议，目前是成为一名地球科学家的非常令人兴奋的时期。地球形成于约46亿年前，由早期太阳系中存在的尘埃和岩石物质粒子组成。仅仅在几百万年后，地球经历了一次大规模的重组，从一大堆未经分类的原始物质，变成了一颗由中心的金属核心和周围的岩石外部组成的行星。我们仍然不清楚这是如何发生的，因为地球经历了一系列隐藏了大量证据的地质事件。一种可能性是，当地球还处于高温和熔融状态时，液态金属从地球的其余部分分离出来，下降到地球的中心，形成了地球的核心。在这个过程中，地球上的大部分铁和许多其他元素优先分配到金属核心中。这给地球外部的岩石部分带来了一种特有的化学信号，我们可以通过火山喷发的岩石来采集这种信号。然而，地球历史的这一部分有许多方面是我们不了解的。例如，我们不知道内核形成的确切条件，也不知道它如何影响行星化学的其他方面，例如行星岩石内部存在的氧气量。如果我们想要了解地球上的生命是如何起源的，这是一个需要回答的重要问题，因为地球上的海洋和大部分大气很可能是在地球还很年轻的时候就从行星内部泄漏出来的气体。我的项目旨在了解地核是在什么条件下形成的，以及这是如何影响地球岩石内部存在的氧气量的。它利用模拟地核形成时地球内部存在的非常高的压力和温度的实验，结合对这些实验进行的非常精确的化学分析。从这些结果中，我将了解某些化学元素是如何在金属核心和地球岩石外部之间分配的，以及这种分配行为是否会随着不同的条件和存在的氧气量而变化。通过将我从实验中获得的结果与来自地球的岩石和非常原始的陨石的化学成分进行比较，我们将能够更好地了解地核是如何形成的，以及这可能如何影响我们星球的化学以及其大气和海洋的发展。

We know very little about the origin of our own planet, how it has evolved through time and how it came to be suitable for life. There is considerable controversy surrounding issues like climate change, and the search for new planets around stars other than the Sun and missions to planets in our own solar system and it is currently a very exciting time to be an Earth scientist. The Earth formed about 4600 million years ago, from particles of dust and rocky material present in the early solar system. Only a few million years later, the Earth underwent a massive reorganisation from an enormous mass of unsorted primitive material into a planet composed of a metal core in its centre and a surrounding rocky outer part. We still do not understand precisely how this happened, as the Earth has undergone a wide range of geological events which hide much of the evidence. One possibility is that when the Earth was still hot and molten, liquid metal separated from the rest of the planet and descended to the centre of the Earth, forming its core. During this process, most of the Earth's iron and many other elements were distributed preferentially into the metal core. This imparted a characteristic chemical signal to the outer rocky parts of the Earth, which we can sample through rocks erupted from volcanoes. However, there are many aspects of this part of Earth history that we do not understand. For example, we do not know the exact conditions of core formation and how it could have affected other aspects of the planet's chemistry, such as the amount of oxygen present in the rocky interior of the planet. This is an important question to answer if we are to understand how life originated on Earth, as it is likely that the Earth's oceans and much of the Earth's atmosphere originated from gases leaking out of planet's interior when the Earth was still very young. My project is aimed at understanding what kind of conditions the Earth's core formed under and how this affected the amount of oxygen present in the rocky interior of the Earth. It uses experiments which simulate the very high pressures and temperatures that would have been present in the Earth's interior when the core formed, combined with very precise chemical analyses of these experiments. From these results I will learn how certain chemical elements distributed themselves between the metal core and the rocky outer part of the Earth, and whether this distribution behaviour changes with different conditions and with the amount of oxygen present. By comparing the results I get from the experiments with the chemical compositions of rocks from the Earth and very primitive meteorites we will be able to understand better how the Earth's core formed, and how this may have affected the chemistry of our planet and the development of its atmosphere and oceans.