Osmium and Tungsten Isotopes Reveal Earth’s Youthful Exuberance

The siderophile elements, which include Re, Pt, Os, and W, directly constrain the accretionary history of Earth. The largely chondritic 186,187Os/188Os ratios of Earth’s mantle, coupled with excesses in siderophile element abundances, provide nearly incontrovertible evidence that some meteoritic addition continued after core formation was complete. Osmium and W isotope systematics of plume-derived mafic-ultramafic rocks reveal the complex chemical evolution of their deep mantle sources. In the upper mantle, Re-Os dating of whole-rock xenoliths and sulfide inclusions in diamonds hosted by kimberlites indicate both ancient melt depletion and subsequent modification of the mantle lithosphere beneath the earliest continents, with Re-Os ages of eclogitic diamonds possibly recording the transition to a sustained plate tectonic regime on Earth.