A collaborative team of researchers from China and Switzerland conducted an experiment suggesting that the Earth’s core may harbor an immense quantity of hydrogen, potentially equivalent to 45 times the volume of all the world’s oceans. This finding challenges the long-held theory suggesting that our planet’s water primarily arrived via cometary impacts. For a considerable time, scientists have observed that the density of the Earth’s core is lower than that of pure iron, implying the presence of lighter elements, hydrogen among them.
Although much of the Earth’s surface is covered by water—a molecule containing hydrogen—several studies propose that the main stores of this element are sequestered deep within the planet, dating back to its formation approximately 4.5 billion years ago. Precise quantification of hydrogen within the core has always been difficult due to the extreme conditions and inaccessibility of these depths.
To circumvent these obstacles, a scientific group from Peking University and ETH Zurich utilized an innovative methodological approach. Their study, documented in Nature Communications, involved laser heating within diamond anvil cells to replicate the pressures and temperatures found deep within the planet. Unlike prior techniques relying on X-ray diffraction, which were prone to significant errors, this team concentrated on simulating the separation processes between metal and silicate materials.
During the experiment, iron samples (mimicking core material) and hydrated silicate glass (representing the ancient magma ocean) were subjected to pressures reaching 111 gigapascals and temperatures up to 6,000 degrees Celsius. This successfully modeled melting processes akin to those during early planetary accretion. Atomic Probe Tomography (APT) was then employed to analyze the results, enabling the creation of a three-dimensional map of the samples’ composition at the nanoscale.
The researchers paid close attention to silicon-oxygen-hydrogen (Si-OH) rich nanostructures that materialized during the process. Their analysis revealed that the molar ratio of silicon to hydrogen within these structures closely approached 1:1.
By extrapolating these laboratory findings to the entire planet, the investigators estimated that the Earth’s core constitutes between 0.07% and 0.36% hydrogen by mass. Converted to volume, this suggests enough water could be stored to fill anywhere from 9 to 45 planetary oceans. This magnitude reinforces the hypothesis that the core represents our planet’s largest hydrogen reservoir.
This discovery carries significant implications for understanding the genesis of Earth’s water. If the bulk of hydrogen resides in the core, it favors an internally derived origin—meaning the hydrogen was incorporated during the initial accretion stages of planet formation. This stands in contrast to the competing theory of late delivery through impacts by comets that struck Earth after its crust had solidified.
“The premise that Earth’s hydrogen, including that in the core, was delivered during the planet’s formation is well supported,” commented lead author Dongyang Huang from Peking University. “What causes debate within the scientific community is the precise stage at which this incorporation occurred.”
The paper’s authors acknowledge certain limitations in their work. For instance, residual hydrogen within the tomography chamber may have slightly skewed the measurements, and there remains uncertainty regarding the exact concentration of silicon in the core. Nevertheless, the data obtained establish exciting new avenues for investigating deep-Earth geochemistry and the formative history of our planet.
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