Tracing isotopic heterogeneities in the Early Earth’s mantle through time

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Differentiation of Earth into a metallic core and a rocky mantle as well as the onset of modern-style mantle convection are probably amongst the most pervasive transformations our planet has endured. These early planetary-scale processes were essential in converting the Earth into a habitable realm. On its surface, the Earth’s intricate internal geodynamic system leads to the formation of rift systems and subduction zones, which play an important role in the global material cycle, for instance in controlling the carbon- and sulfur content in its atmosphere over geological timescales. Yet, how and when modern-style mantle convection evolved within the first billion years after the accretion of the Earth remains enigmatic. Studying core formation and early mantle convection are research strands that are intertwined in a rather peculiar way: Separation of metallic melt from a silicate magma ocean during core formation caused an almost quantitative transfer of so-called siderophile elements from the mantle into the core leaving a diagnostic chemical and isotopic signature in the earliest rocks that formed on Earth. Shortly after core formation was completed, the Earth was struck by a limited number of cataclysmic meteorite impacts that injected a small amount of fresh sideropile elements into the mantle, thus partly replenishing their abundances in the silicate Earth. Here, we will be using this planetary-scale tracer experiment to shed light on the internal isotopic heterogeneity of the Early Earth by trying to identify, how this meteoritic material mixed into the Earth’s mantle over a timescale of about 1 billion years. We will start by analysing the oldest rocks on Earth in order to characterise the isotopic signature that core formation imparted on the siderophile elements in the silicate mantle before the meteoritic material was completely homogenised. We will then analyse rocks from crucial time periods throughout Earth’s history to see, over which timescales the newly arrived siderophile elements were mixed into the Earth’s mantle. Our findings, together with other evidence gathered as part of the project "Building a Habitable Planet", will enable a better and more detailed characterisation of the processes involved in the evolution of Early Earth mantle convection.