Earth’s Core May Hold Hidden Reservoirs of Helium

Using a laser-heated diamond anvil cell, they observed this unexpected interaction, suggesting that vast amounts of helium may be present in the Earth’s core. This finding challenges long-held theories about the planet’s internal structure and history and could provide new insights into the primordial nebula from which our solar system originated, the journal Physical Review Letters reported.

Volcanic eruptions primarily release rocks and minerals, but they can also emit traces of a rare gas known as primordial helium. Unlike the more common isotope, helium-4 (⁴He), which consists of two protons and two neutrons and is continuously produced by radioactive decay, primordial helium—helium-3 (³He)—contains only one neutron and is not formed on Earth. Its presence offers valuable clues about the planet’s deep interior and its connection to cosmic origins.

Given the occasionally high 3He/4He ratios found in volcanic rocks, especially in Hawaii, researchers have long believed there are primordial materials containing 3He deep within the mantle. However, graduate student Haruki Takezawa and members of Professor Kei Hirose’s group from the University of Tokyo’s Department of Earth and Planetary Science have now challenged this view with a new take on a familiar experiment: crushing things.

“I have spent many years studying the geological and chemical processes that take place deep inside the Earth. Given the intense temperatures and pressures at play, experiments to explore some aspects of this environment must replicate those extreme conditions. So, we often turn to a laser-heated diamond anvil cell to impart such pressures on samples to see the result,” said Hirose. “In this case, we crushed iron and helium together under about 5-55 gigapascals of pressure and at temperatures of 1,000 kelvins to nearly 3,000 kelvins. Those pressures correspond to roughly 50,000-550,000 times atmospheric pressure and the higher temperatures used could melt iridium, the material often used in car engine spark plugs due to its high thermal resistance.”

Previous studies have shown only small traces of combined iron and helium, in the region of seven parts per million helium within iron. But in this case, they were surprised to find the crushed iron compounds contained as much as 3.3% helium, about 5,000 times higher than previously seen. Hirose suspects this is at least in part due to something novel about this particular set of experiments.

“Helium tends to escape at ambient conditions very easily; everyone has seen an inflatable balloon wither and sink. So, we needed a way to avoid this when taking our measurements,” he said. “Though we carried out the material syntheses under high temperatures, the chemical-sensing measurements were done at extremely cold, or cryogenic, temperatures. This way prevented helium from escaping and allowed us to detect helium in iron.”

This finding has implications for understanding Earth’s origins. The presence of helium in the core suggests the young Earth likely captured some gas from the solar nebula of hydrogen and helium that surrounded the early solar system. This could also mean that some of Earth’s water may have come from hydrogen in this ancient gas, offering a new perspective on the planet’s early development.

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