A research team has produced the first direct experimental evidence that Earth’s iron core traps hydrogen inside nanoscale structures, a finding that supports a long-debated hypothesis: the deepest layer of the planet may contain more hydrogen than all of its surface oceans combined. The study, published in Nature Communications, used extreme laboratory conditions to simulate the core and then imaged individual atoms locked within the metal, offering a level of detail that prior work could not achieve. If the results hold up under further scrutiny, they stand to reshape how scientists account for water and other volatile elements across Earth’s history.
Squeezing Iron to See Hidden Atoms
The new experiments pushed tiny samples of iron and silicate to pressures reaching roughly 111 gigapascals and temperatures near 5,100 Kelvin, conditions that approximate the boundary between Earth’s mantle and outer core. Researchers accomplished this using laser-heated anvil cells, a technique that compresses materials between two gem-quality diamonds while a laser heats the target to thousands of degrees. After quenching the samples, the team applied atom probe tomography, a method that strips away material one atom at a time and maps each element’s position in three dimensions. Inside the iron, they found hydrogen concentrated alongside silicon-oxygen-rich nanostructures, with a near-unity molar ratio of silicon to hydrogen. That ratio suggests hydrogen does not simply dissolve uniformly through molten iron but instead clusters in specific chemical neighborhoods, a behavior that had been predicted by theory yet never directly observed at these conditions.
This clustering matters because it changes how scientists estimate total hydrogen storage capacity. A uniform distribution would cap the amount of hydrogen that iron can hold; a structured, nanostructure-hosted arrangement could accommodate far more. The observation that hydrogen and silicon-oxygen features appear together also hints at the chemical pathway by which hydrogen entered the core billions of years ago, when molten iron separated from silicate rock during planetary formation. If hydrogen preferentially followed silicon into the metal, as the new atomic-scale images imply, then early Earth may have sequestered a substantial fraction of its original water inventory into the core rather than leaving it at the surface.
Decades of Clues Pointing to a Hydrogen-Rich Core
The idea that hydrogen hides deep inside the planet is not new. A classic Nature study from 1977 first proposed hydrogen as a candidate light element that could explain why the outer core is roughly 10 percent less dense than pure iron-nickel alloy. That density deficit has puzzled geophysicists for generations: something lightweight must be mixed in, and hydrogen, the lightest element of all, is a natural suspect. Early high-pressure measurements at about 7.5 gigapascals confirmed that hydrogen dissolves into iron and that its partitioning behavior is temperature-dependent, meaning hotter conditions during core formation would have driven even more hydrogen into the metal.
Subsequent experiments at 30 to 60 gigapascals and 3,100 to 4,600 Kelvin reported a metal-silicate partition coefficient for hydrogen of at least 29, meaning iron absorbs hydrogen roughly 29 times more readily than the surrounding silicate melt. Those results, reported in modern partitioning experiments, led researchers to estimate that 0.3 to 0.6 weight percent hydrogen could have been incorporated into the core during formation. Even the lower end of that range translates to an enormous mass of hydrogen, given that the core accounts for about a third of the planet’s total mass. Independently, ab initio simulations have confirmed hydrogen’s strong affinity for iron at core-formation pressures, reinforcing the case that the core could store water equivalents exceeding the oceans. The new nanoscale imaging does not replace these earlier lines of evidence, but it anchors them in direct observations of how hydrogen actually sits inside solidified core-like material.
Why the Core’s Composition Shapes the Magnetic Shield
The stakes extend well beyond geochemistry. Earth’s magnetic field, generated by convection currents in the liquid outer core, depends on the core’s composition and thermal state. Light elements dissolved in the iron alloy influence how heat and matter circulate, which in turn controls the strength and stability of the geodynamo. A computational study evaluating density and seismic velocity constraints at the inner-core boundary concluded that hydrogen and silicon likely dominate the light-element inventory under its model, with quantitative best-fit estimates for hydrogen content in both the outer and inner core. If hydrogen is indeed a major light element, it would be a key ingredient sustaining the magnetic field that shields the surface from solar radiation.
That connection carries real consequences. The geodynamo effect protects Earth by deflecting charged particles streaming from the Sun, and the magnetic field it produces is generated by circulating molten iron in the core. Any shift in the core’s chemical makeup over geological time could alter convection patterns and, by extension, the field’s intensity. Research into the coupled evolution of the deep interior and surface oceans suggests the core may have maintained a partially molten state in the deep mantle more than 2 billion years ago, a timeline that aligns with major changes in Earth’s magnetic record. In that framework, hydrogen-rich nanostructures inside the core alloy are not merely curiosities: they are part of the physical system that governs how efficiently the planet cools, and how long its magnetic shield can endure.
Rewriting Earth’s Volatile Budget
One of the sharpest tensions in planetary science is the so-called volatile budget problem: scientists cannot fully account for the hydrogen, carbon, nitrogen, and noble gases that Earth acquired during accretion. Isotopic and abundance analyses of Earth’s volatile inventories have long pointed to a mismatch between what chondritic meteorites delivered and what remains visible in the oceans, atmosphere, and crust. Traditional models assumed that most hydrogen and other volatiles resided near the surface, with only modest amounts locked into the mantle and very little in the core. The emerging picture of a hydrogen-bearing core upends that assumption by suggesting that the deep interior may hide a vast, previously uncounted reservoir.
If the core contains several ocean masses’ worth of hydrogen, as some estimates based on partitioning experiments and simulations allow, then Earth’s total water budget becomes far larger than surface observations imply. That, in turn, reshapes debates over where Earth’s water came from and how quickly it was delivered. A core that sequesters large quantities of hydrogen could reconcile apparent discrepancies between meteorite-derived delivery scenarios and the current surface inventory, because much of the original hydrogen would simply be out of sight, locked into metallic structures at the planet’s center. It also raises the possibility that hydrogen exchange between the core, mantle, and surface has evolved over time, subtly influencing long-term climate stability and the persistence of oceans.
What Comes Next for Deep-Earth Hydrogen Research
For now, the new atom-scale images provide a crucial but still incomplete snapshot of hydrogen in core-like materials. The experiments capture what happens when iron and silicate are compressed and heated to core-mantle boundary conditions, then rapidly cooled, but they cannot yet reproduce the full complexity of a vigorously convecting, slowly cooling core over billions of years. Future work will need to test whether similar nanoscale structures form under slightly different pressure-temperature paths, and whether additional light elements such as carbon, sulfur, or oxygen alter the way hydrogen is stored. Seismological observations, which probe the core’s density and sound speeds, will also continue to serve as an independent check on how much hydrogen can plausibly be hidden there.
Despite these open questions, the convergence of decades of partitioning experiments, theoretical calculations, and the latest nanoscale imaging is steadily eroding the idea of a simple, hydrogen-poor core. Instead, Earth’s center increasingly looks like a dynamic alloy where light elements are organized into intricate structures that influence everything from the planet’s volatile budget to the longevity of its magnetic shield. As researchers refine their models and extend experiments to ever more realistic conditions, the hydrogen trapped in those tiny structures may prove to be one of the most consequential, if inaccessible, components of the planet we live on.
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*This article was researched with the help of AI, with human editors creating the final content.
