Huge reserves of helium from the Big Bang that remain in the core suggest that the Earth formed in a solar nebula. Helium-3, a rare isotope of helium gas, is leaking from the Earth’s core, according to a new study. Because almost all of Sun-3 comes from the Big Bang, the gas leak adds evidence that the Earth formed inside a long-discussed solar nebula. Helium-3 has been measured on the Earth’s surface in relatively small quantities. But scientists did not know how much leaked from the Earth’s core, unlike its middle layers, called the mantle. The new study, published today (March 28, 2022) in Geochemistry Geophysics Geosystems, identifies the nucleus as the primary source of helium-3 on Earth. Some natural processes can create helium-3, such as radioactive decay of tritium, but helium-3 is mainly produced in nebulae – huge, rotating clouds of gas and dust, like the one created by our Solar System. Because the sun is one of the first elements produced in the universe, most of the helium-3 can be detected in the Big Bang. As a planet grows, it accumulates material from its environment, so its composition reflects the environment in which it was formed. In order to have high concentrations of helium-3 deep in the core, the Earth would have to form in a thriving solar nebula, not on its fringes or during its waning phase. New research adds further clues to the mystery surrounding Earth formation, adding to the theory that our planet formed in the solar nebula. The study was published in the journal AGU Geochemistry, Geophysics, Geosystems, which publishes research on the chemistry, physics, geology and biology of the Earth and planetary processes. About 2,000 grams of helium-3 leak from Earth each year, “about enough to fill a balloon the size of your office,” said study lead author Peter Olson, a geophysicist at the University of New Mexico. “It’s a miracle of nature, and an indication of Earth’s history, that there is still a significant amount of this isotope inside the Earth.” The researchers modeled the sun during two key stages in Earth’s history: the early formation, when the planet was accumulating sun, and the formation of the Moon, after which the sun disappeared. Evidence suggests that an object about one-third the size of Earth hit the planet early in its history, about 4 billion years ago, and that the impact would have repeated the Earth’s crust, allowing much of the sun to escape. The gas continues to escape to this day. Using the modern helium-3 leakage rate along with models of helium isotope behavior, the researchers estimated that there were 10 tegrams (1013 grams) to one kilogram (1015 grams) of helium-3 in the nucleus – a huge amount that Olson points out in its formation. Earth in the solar nebula, where high concentrations of gas would allow it to accumulate deep on the planet. However, future research into other gases created by nebulae, such as hydrogen, which leak at similar rates and locations as helium-3, could be a “smoking weapon” for the nucleus as a source, Olson said. “There are many more mysteries than certainties.” Reference: “Primordial Helium-3 Exchange Between Earth’s Core and Mantle” by Peter L. Olson and Zachary D. Sharp, March 28, 2022, Geochemistry Geophysics Geosystems.DOI: 10.1029 / 2021GC009985
