Linking the Core Heat Content to Earth's Accretion History

Abstract

AbstractIn this study we use a parameterized model of differentiation in a magma ocean setting, in which the magma ocean depth evolves during accretion, to predict the composition of the primordial core. We couple this chemical model to a thermal evolution model of the accreting metal to estimate the Earth's core heat content at the end of its formation. We find geochemically consistent models. All these scenarios have in common two key features: (a) the average pressure of metal‐silicates equilibration is between 20 and 45 GPa (final pressure between 40% and 60% of CMB pressure); (b) 60%–80% of Earth's mass is accreted as reduced material. The chemical stratification is stable in most cases, though some scenarios result in an unstable compositional stratification. Mixing an initially stratified core requires a small fraction of the energy released after a giant impact. Importantly, the temperature at the Core Mantle Boundary is ranging from 3925 to 4150 K. For example, scenarios in which the magma ocean remains shallow for a large part of the accretion, then gets deeper at the end of accretion can produce chemically coherent models with cooler cores. This suggests that independent constraints on the core temperature could in principle be used as constraints for the differentiation conditions, and core composition. In particular, we find that the abundance of light elements in the core correlates positively with the temperature of the core at the end of accretion, as well as with the average pressure of equilibration during differentiation.