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New Insights into Helium’s Role in Earth’s Core

Researchers have succeeded in creating a new compound that includes helium, one of the most uncooperative elements in the universe. This innovative compound, as reported on February 25 in Physical Review Letters, incorporates helium atoms into crystalline iron, potentially revealing new aspects of helium’s role in Earth’s geology.

Helium, known for its lack of reactivity, typically refrains from forming chemical bonds. However, under extreme conditions of pressure and temperature, it can interact with select elements, including the newly studied iron. This interaction suggests that helium from the early solar system could reside within the iron core of our planet.

To produce this compound, a team led by physicist Kei Hirose from the University of Tokyo utilized a diamond anvil cell, a device capable of generating immense pressures exceeding 50,000 times that of Earth’s atmosphere alongside temperatures surpassing 1,000 degrees Celsius. The resulting crystals demonstrated an increased volume compared to those of pure iron, attributed to helium ions fitting into the spaces between iron atoms.

Exploring Helium’s Stability

Despite being incorporated into the crystalline structure, helium does not form direct bonds with iron due to its inherently unreactive nature. According to chemist Stefano Racioppi from The State University of New York at Buffalo, “Helium is very happy as it is. It doesn’t want to share an electron,” indicating that helium can still function within these advanced compounds without forming conventional bonds.

This new discovery has possible implications for understanding helium’s distribution within the Earth. The majority of helium found on our planet comes from radioactive decay processes in elements like uranium, but some volcanic eruptions release primordial helium, which originated shortly after the Big Bang. This raises the question of whether Earth’s core may contain a deep reservoir of primordial helium.

Hirose emphasizes that the next steps involve determining the helium’s stability in iron compared to silicates in the mantle. The key lies in understanding how helium partitions between magma, silicate melts, and metallic iron. This information could indicate whether helium prefers a residence in the core or in higher mantle layers.

Implications for Noble Gas Chemistry

Ronald Cohen, a computational physicist at the Carnegie Institution for Science, adds a cautious note, stating that while the findings do not definitively prove the existence of helium in the Earth’s core, they suggest it is a plausible scenario. This development opens up new avenues in the field of noble gas chemistry, sparking curiosity about whether similar interactions can occur with other transition metals.

As Maosheng Miao from California State University, Northridge points out, exploring the formation of helium compounds with different metals could introduce entirely new chemical phenomena that have yet to be considered, expanding our understanding of both chemistry and geology.

The implications of this groundbreaking research may extend beyond academic interest, potentially altering our perceptions of the Earth’s composition and the role of elemental interactions in geological processes.

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