Zachary D. Sharp

Volatiles from the solar nebula are known to be present in Earth's deep mantle. The core also may contain solar nebula‐derived volatiles, but in unknown amounts. Here we use calculations of volatile ingassing and degassing to estimate the abundance of primordial 3 He now in the core and track the rate of 3 He exchange between the core and mantle through Earth history. We apply an ingassing model that includes a silicate magma ocean and an iron‐rich proto‐core coupled to a nebular atmosphere of solar composition to calculate the amounts of 3 He acquired by the mantle and core during accretion and core formation. Using experimentally determined partitioning between core‐forming metals and silicate magma, we find that dissolution from the nebular atmosphere deposits one or more petagrams of 3 He into the proto‐core. Following accretion, 3 He exchange depends on the convective history of the coupled core‐mantle system. We combine determinations of the present‐day surface 3 He flux with estimates of the present‐day mantle 3 He abundance, mantle and core heat fluxes, and our ingassed 3 He abundances in a convective degassing model. According to this model, the mantle 3 He abundance is evolving toward a statistical steady state, in which surface losses are compensated by enrichments from the core.