Thorsten Kleine reports that a late veneer of meteoritic material, added after Earth core had formed, may be the source of our noble metals. Its absence from some parts of Earth mantle will now force a rethink about this late accretion. Earth metallic core is the major repository of the highly siderophile - i.e., iron-loving - elements, which include gold, rhenium and the platinum-group elements. Their strong affinity for iron means that their abundance in Earth mantle is very low but not as low as might be expected. One popular explanation for this discrepancy is that a late veneer of primitive meteoritic material was added to Earth mantle after core formation had ceased. On page 195 of this issue, Willbold and colleagues add weight to this theory by using an isotope of tungsten to show that the late veneer is missing from some areas of the mantle. Our understanding of Earth late accretion may need to change as a result. Energetic collisions between Moon to Mars-sized planetary embryos during Earth growth caused widespread melting, facilitating the separation of molten metal from surrounding liquid silicate in a magma ocean. The molten iron sank towards Earth center, removing the siderophile elements to the core. However, highly siderophile elements are present in Earth mantle in much higher amounts than are predicted from metal silicate partition experiments at atmospheric pressure.
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