Deep beneath our feet, at the very center of the planet, lies what may be the largest reservoir of hydrogen on Earth — not locked in water or rock, but dissolved within the metallic core itself.
Researchers used extreme laboratory conditions to simulate how Earth’s core formed billions of years ago and measured how much hydrogen was trapped inside it. The core is estimated to hold between 0.07 and 0.36 percent hydrogen by weight — equivalent to somewhere between 9 and 45 oceans of water, researchers report February 10 in Nature Communications.
The finding challenges the long-held picture of Earth as a cosmochemically “dry” planet. Previous estimates of hydrogen in the core have spanned four orders of magnitude, from 10 to 10,000 parts per million, largely because measuring hydrogen under the crushing pressures and extreme temperatures deep inside the Earth is extraordinarily difficult. Until now, most estimates relied on indirect methods — inferring hydrogen content from how the element expands iron’s crystal lattice. This study offers a more direct window into the problem, with the researchers concluding that their work reveals hydrogen is “strongly coupled with the high-pressure sequestration” of other elements in the core.
To reach these findings, the team at ETH Zürich and Peking University squeezed iron metal and water-bearing silicate glass together inside a laser-heated diamond anvil cell, generating pressures up to 111 gigapascals and temperatures exceeding 5,000 Kelvin — conditions comparable to those inside a forming Earth. When the molten metal and silicate equilibrated, hydrogen, silicon and oxygen all migrated together into the metal. Upon cooling, these elements clustered into tiny nanoscale structures just tens of nanometres across.
The researchers then carved these recovered samples into needle-shaped tips and subjected them to atom probe tomography, a technique that strips atoms one by one from a sample and identifies each by its mass. This allowed them to map, in three dimensions, exactly where hydrogen atoms resided — and confirmed that hydrogen was genuinely present inside the iron, bound up alongside silicon and oxygen rather than being a contaminant from the instrument. Crucially, the molar ratio of silicon to hydrogen in these clusters was close to one-to-one, giving the team a new way to estimate the core’s hydrogen budget based on its better-constrained silicon content.
Citations
D. Huang et al. Experimental quantification of hydrogen content in the Earth’s core. Nature Communications. Published online February 10, 2026. DOI: 10.1038/s41467-026-68821-6
