The Earth’s interior is far more complex than previously understood. A new study suggests the planet’s core, long considered a massive sphere of iron and nickel, may also be a significant reservoir of hydrogen – potentially holding the equivalent of 9 to 45 oceans of water locked within its metallic structure.
Researchers at ETH Zurich, led by Professor Motohiko Murakami, conducted laboratory experiments simulating the extreme pressures and temperatures of Earth’s formation to arrive at this surprising conclusion. Their work, published in the journal Nature Communications, proposes that hydrogen entered the core early in Earth’s history, traveling alongside silicon and oxygen as the planet differentiated into layers.
Understanding the composition of Earth’s core is notoriously difficult. Direct sampling is impossible, and interpreting seismic data – the primary tool for probing the interior – is complicated by the extreme conditions present deep within the planet. To overcome these challenges, the team employed a laser-heated diamond anvil cell, a device capable of recreating the immense pressures and temperatures found at the Earth’s core-mantle boundary.
“Using state-of-the-art tomography, we were finally able to visualise how these atoms behave within metallic iron,” said Dongyang Huang, a former postdoctoral researcher and first author of the study. The experiment involved melting iron within a water-bearing crystal capsule and observing how hydrogen, oxygen, and silicon interacted with the liquid metal. Researchers then rapidly “froze” the sample to analyze the distribution of these elements.
How Hydrogen is ‘Packed’ into the Core
The key finding is that hydrogen doesn’t exist as free gas or water molecules within the core. Instead, it chemically bonds with the iron, forming iron hydrides intertwined with silicon- and oxygen-rich nanostructures. This “packing” mechanism explains how hydrogen could have been transported to the core during the planet’s early formation, rather than being confined to the surface.
By combining the hydrogen-to-silicon ratio measured in their experiments with existing estimates of silicon abundance in the core, the researchers calculated that hydrogen constitutes approximately 0.07% to 0.36% of the core’s mass. While seemingly small, this percentage translates to a substantial amount of hydrogen when considering the core’s immense size – equivalent to roughly 9 to 45 oceans of water, according to the study.
Implications for Earth’s History and Beyond
This discovery has significant implications for our understanding of Earth’s water origins. Scientists have long debated whether Earth’s water arrived later, delivered by comets and asteroids, or was present during the planet’s initial formation. This research lends support to the latter theory, suggesting a substantial supply of hydrogen was already present when the core formed. This doesn’t rule out contributions from external sources, but suggests they may not be the primary origin of Earth’s water.
The presence of hydrogen deep within the Earth could also influence several key planetary processes. The ETH Zurich team suggests potential links to the generation of Earth’s magnetic field, mantle convection, and the long-term cycling of hydrogen between the deep interior and the surface.
understanding how hydrogen behaves under extreme pressure is crucial for modeling the interiors of rocky exoplanets. The composition of a planet’s core – including the presence of light elements like hydrogen – significantly impacts its formation and evolution. Professor Murakami’s research group at ETH Zurich has been heavily involved in developing the advanced spectroscopic measurement systems used in this research, as detailed on the Experimental Mineral Physics group website.
While the “dozens of oceans” headline is attention-grabbing, the estimate relies on a complex chain of evidence – laboratory measurements, structural analysis, and assumptions about core composition. Future research will focus on refining these estimates and testing the scalability of lab results to a planetary system. Professor Murakami is a leading expert in experimental mineral physics, with over 4,724 citations to his work, according to Google Scholar.
this research highlights that the water we see on Earth’s surface may represent only a small fraction of the planet’s total hydrogen inventory, with a vast reservoir hidden deep within the core. “The water we see on the Earth’s surface today may be just the visible tip of a gigantic iceberg deep inside the planet,” Murakami said.
What comes next for this line of research is further refinement of the models used to estimate core composition and the development of even more sophisticated experimental techniques to probe the Earth’s deep interior. The findings underscore the importance of continued exploration into the mysteries hidden beneath our feet.
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