The Earth’s core is often described as simply a giant ball of iron and nickel. Now, new research claims it’s also the primary storage location. hydrogenPerhaps dozens of oceans’ worth of water is trapped in metal deep beneath our feet.

In this paper, researchers led by Motohiko Murakami of ETH Zurich conducted a laboratory experiment designed to simulate the intense pressure and heat present during Earth’s formation. They concluded that hydrogen likely entered the core early and moved along with silicon and oxygen as the planet’s interior separated into layers.

How do we find hydrogen where we can’t sample it?

You can’t reach the core with a drill. seismic waves That helps, but the conditions in the core are so extreme that it’s difficult to match laboratory data with the real Earth. So the team used a laser-heated diamond anvil cell to recreate the core-forming conditions. Two tiny diamonds squeeze the sample at a pressure far greater than the surface pressure, and a laser raises its temperature to thousands of degrees.

In their setup, a small piece of metal iron was placed inside a crystal capsule containing water. As the iron melted, hydrogen, oxygen, and silicon migrated into the liquid metal. The researchers then quickly “frozen” the sample so they could study where the atoms ended up. The difficult part was spotting hydrogen, the lightest element, inside the dense metal under these conditions.

“Using state-of-the-art tomography, we were finally able to visualize how these atoms behave within metallic iron,” said Dongyang Huang, a former postdoctoral researcher and lead author of the study.

The key result is that hydrogen is chemically “packed” into the core material. Hydrogen is never present in the core as free gas or water molecules. Instead, it becomes part of the metal itself, forming iron hydrides bound to silicon- and oxygen-rich nanostructures within the iron alloy.

This part is important because it provides a mechanism for how hydrogen is transported downward during nucleation rather than remaining near the surface.

Using laboratory-measured hydrogen-to-silicon ratios and combining them with previous estimates of how much silicon is in Earth’s core, the researchers estimated that hydrogen makes up about 0.07% to 0.36% of the core’s mass. The percentage may seem small, but the core is huge. In “water” terms, this estimate corresponds to approximately 9 to 45 oceans of water (some summaries say up to about 45 oceans).

A new angle on where Earth’s water comes from

Scientists have long debated whether most of Earth’s water arrived late, carried by comets and asteroids after the core was formed, or whether much of it was present during Earth’s main building stages. This study supports the second theory. In other words, if that much hydrogen reached the core, it is likely that a large amount of hydrogen existed initially during the core’s formation, not just after the fact.

That doesn’t mean the comet didn’t deliver anything. At least if the new core count is maintained, it suggests that delivery delays may not be the main culprit.

Deeply stored hydrogen can impact several large Earth systems over long timescales. The ETH team points to possible connections between how the core generates Earth’s magnetic field, how the mantle moves, and how hydrogen slowly circulates between the Earth’s depths and the surface over billions of years.

You also get broader benefits. Knowing how hydrogen behaves in metals under high pressure can help researchers model rocky exoplanets. The mix of light elements in a planet’s interior can influence whether a planet forms a metallic core and how it evolves.

Despite the fancy headline “Dozens of Oceans,” this estimate is based on a body of evidence: laboratory measurements, microstructural imaging, and assumptions about the composition of the core from past studies. The next step is to test how robust these links are. In particular, we test how well the lab results map onto a globally messy system.

Still, this message is hard to ignore. The water we see on the Earth’s surface represents only a small portion of the Earth’s total hydrogen, most of which may be hidden in places we can’t reach within the core itself.

“This discovery deepens our understanding of the deep Earth,” Murikami said. “They provide clues about how water and other volatile substances were distributed in the early solar system and how Earth acquired its hydrogen…The water we see on Earth’s surface today may be just the visible tip of a huge iceberg deep within the Earth.”

The research results were published in a magazine nature communications.