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Accretion, Composition and Core-Mantle Differentiation of the Earth

Friday, November 20, 2009
Dave
Rubie (University of Bayreuth, Germany)

A model of core formation is presented in which the Earth accretes heterogeneously through a series of impacts with smaller differentiated bodies. Each collision results in the impactor's metallic core reacting in a magma ocean before merging with the Earth's proto-core. Based on a least squares fit to the primitive terrestrial mantle composition, the initial 60-70% of the Earth accretes from highly-reduced material with the final 30-40% of accreted mass being more oxidized. The larger impactor cores fail to re-equilibrate completely before merging with the proto-core. Estimated re-equilibration conditions may be consistent with magma oceans extending to the core-mantle boundary, thus making core formation extremely efficient. The results are consistent with approximately 70% of the Moon being derived from the final giant impactor.

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