Earth's core may have been leaking hydrogen for billions of years

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When Earth formed billions of years ago, its metallic core was wrapped in a global ocean of molten rock, which eventually cooled and crystallized to form the mantle. Today, when deep-rooted mantle plumes rise toward the surface and produce volcanic eruptions, the resulting lava can contain hydrogen from deep inside the planet.

Hydrogen comes in two stable forms, standard light hydrogen and a heavier version called deuterium. While most volcanic rocks have relatively normal hydrogen isotope ratios, some lavas associated with deep mantle plumes contain an unusually low proportion of deuterium. That rare mix has provoked a major debate: Did this low-deuterium signature form long ago as the early magma ocean froze, or does it come from hydrogen leaking out of Earth's metallic core?

To try to answer that question, a team of researchers led by Wenzhong Wang at the University of Science and Technology of China used advanced computer simulations to replicate conditions thousands of kilometers beneath the Earth's surface. They examined how the two forms of hydrogen behaved as molten rock cooled and crystallized into different minerals. The team then used the results to model how the two forms of hydrogen would have been distributed through the Earth's early mantle.

In a paper published in the journal Science Advances, the researchers suggest that as ancient magma cooled and crystallized, the two forms of hydrogen were distributed relatively evenly through the mantle. There were some small differences in the ratios at different depths, but nothing like the unusually low levels of deuterium found in volcanic rocks from places like Baffin Island in the Canadian Arctic and Iceland. "Our results demonstrate that magma ocean crystallization does not produce substantial hydrogen isotope fractionation within Earth's mantle," stated the study authors.

That means the freezing of the magma ocean cannot explain those unusual signatures. Therefore, the researchers come down on the side of the leakage from the core explanation. They argue that hydrogen with a low proportion of deuterium has likely leaked from Earth's metallic core into the surrounding mantle over billions of years.

And there's another clue pointing toward the core. Some of these volcanic rocks also have unusually high ratios of helium-3 to helium-4. Helium-3 is a rare form of helium that may have been preserved in Earth's core for billions of years.