Experimental quantification of hydrogen content in the Earth's core

Earth's core has long been speculated to be the largest reservoir of hydrogen (H) on the planet. However, current estimates of its H content involve substantial uncertainties, due to the challenge of quantifying H under extreme conditions. Here, we perform superliquidus metal-silicate partitioning experiments on H using laser-heated diamond anvil cells, and combine it with atom probe tomography. The direct observation of H at silicon- and oxygen-rich nanostructures in the iron alloy indicates coupled sequestration of silicon, oxygen and hydrogen into Earth's core during its formation. With the observed molar Si/H ratio close to unity, Earth's core is estimated to contain 0.07-0.36 wt.% H, equivalent to 9-45 oceans of water. Such an amount would require the Earth to obtain the majority of its water from the main stages of terrestrial accretion, instead of through comets during late addition.