Terrestrial Accretion Under Oxidizing Conditions

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Science  10 Jan 2013:
DOI: 10.1126/science.1227923

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The abundance of siderophile elements in the mantle preserves the signature of core formation. Based on partitioning experiments at high pressure (35 to 74 GPa) and temperatures (3100 to 4400 K), we demonstrate that depletions of slightly (V, Cr) and moderately (Ni, Co) siderophile elements can be produced by core formation under more oxidizing conditions than previously proposed. Enhanced solubility of oxygen in the metal perturbs the metal-silicate partitioning of V and Cr, precluding extrapolation of previous results. We propose that Earth accreted from materials as oxidized as ordinary or carbonaceous chondrites. Transfer of oxygen from the mantle to the core provides a mechanism to reduce the initial magma ocean redox state to that of the present-day mantle, reconciling the observed mantle concentrations of V, Cr and geophysical constraints on light elements in the core.

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