Metal–silicate partitioning of highly siderophile elements during Earth's core formation

Highly siderophile elements (HSEs) are those with such a strong affinity for iron metal that they are expected to be nearly completely removed from the bulk silicate Earth (BSE) during core formation. Their presence in the BSE today in higher-than-expected absolute abundances and chondritic relative abundances is taken as evidence of late accretion, the addition of the final ~0.5–1% of Earth’s mass after core formation ceased. However, the behaviors of most HSEs have not been studied to the extreme conditions of Earth’s core formation. Here we present new experiments on the metal–silicate partitioning of Pd, Pt, Ru, and Rh to >40 GPa and >4000 K. All of these HSEs become significantly less siderophile at these conditions, to such an extent that core formation ought to leave too much of these elements in the BSE. We will discuss implications for the absolute and relative abundances of HSEs and various processes that can help reconcile their observed values.