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

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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.