The constraints placed on three current hypotheses of core formation in the earth by new experimental data on the partitioning of siderophile and chalcophile elements among metallic and silicate phases are discussed. Data on partition coefficients, siderophile abundances in the bulk earth, siderophile abundances in the upper mantle, and mineral-melt partitioning in basalts are reviewed and considered in terms of models involving inefficient core formation, equilibrium between an Fe-S-O metallic liquid and mantle silicates, and heterogeneous accretion/'chondritic veneer'. It is concluded that these three hypotheses can explain gross features of the mantle geochemistry, but none predicts siderophile and chalcophile element abundances to within a factor of two of observed values. Either present understanding of metal-silicate interactions and/or present understanding of the early earth requires revision.
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