Primordial helium extracted from the Earth’s core through magnesium oxide exsolution

Helium is considered a key tracer for processes in Earth’s deep interior as the core is thought to be a reservoir for the primordial isotope ³He. High ³He/⁴He ratios in ocean island basalts fed by mantle plumes are indicative of relatively undegassed reservoirs preserved in the deep mantle. Notably, ocean island basalts with tungsten isotopic and ³He/⁴He anomalies point to possible material contributions from the core. However, it remains unclear how helium is transported from the core to the mantle. Here we use first-principles calculations to show that helium strongly favours entering magnesium oxide at core–mantle boundary conditions. This suggests that magnesium oxide exsolved from the core can deliver appreciable amounts of helium back into the mantle. We also modelled the expected helium flux due to magnesium oxide exsolution since core formation, showing that magnesium oxide exsolved from the core may have continuously supplied helium from the core into the mantle throughout much of Earth’s history, imprinting its primordial helium signature into the mantle materials. Moreover, magnesium oxide exsolution may inherit other distinct geochemical signatures from the core, thereby offering a pathway for probing core processes.