  Highly siderophile elements (HSEs) are strongly depleted in the bulk silicate
Earth (BSE) but are present in near-chondritic relative abundances. The
conventional explanation is that the HSEs were stripped from the mantle by the
segregation of metal during core formation but were added back in
near-chondritic proportions by late accretion, after core formation had ceased.
Here we show that metal-silicate equilibration and segregation during Earth's
core formation actually increased HSE mantle concentrations because HSE
partition coefficients are relatively low at the high pressures of core
formation within Earth. The pervasive exsolution and segregation of iron
sulfide liquid from silicate liquid (the "Hadean matte") stripped magma oceans
of HSEs during cooling and crystallization, before late accretion, and resulted
in slightly suprachondritic palladium/iridium and ruthenium/iridium ratios.
