According to new modeling research, an exceedingly rare kind of helium that was produced just after the Big Bang is leaking out of Earth's metallic core.
The great bulk of this gas in the universe, known as helium-3, is primordial, having formed just after the Big Bang 13.8 billion years ago. Some of this helium-3 would have joined other gas and dust particles in the solar nebula, the huge, whirling, and collapsing cloud hypothesized to have resulted in the formation of the solar system.
According to the researchers, the discovery that Earth's core likely includes a massive pool of helium-3 adds to the evidence that Earth formed amid a thriving solar nebula, rather than on its periphery or during its declining phase.
In a statement, research lead author Peter Olson, a geophysicist at the University of New Mexico, stated that helium-3 is "a wonder of nature, and a clue for the history of the Earth, that there's still a significant amount of this isotope in the interior of the Earth."
Scientists already knew that roughly 4.4 pounds (2 kilograms) of helium-3 escapes from the Earth's interior each year, largely along the mid-ocean ridge system where tectonic plates collide, according to the study, which was published online Mar. 28 in the journal Geochemistry, Geophysics, Geosystems.
This is "about enough to fill a balloon the size of your desk," Olson said.
However, scientists were unsure how much helium-3 came from the core versus the mantle, or how much helium-3 was in Earth's reservoirs.
To investigate, the researchers modeled helium abundance during two critical periods in Earth's history: during the planet's early development, when it was still acquiring helium, and after the formation of the moon, when our planet lost a significant amount of this gas. Scientists believe the moon formed some 4 billion years ago when a massive asteroid the size of Mars crashed with Earth.
This catastrophe would have melted Earth's crust, allowing much of the helium contained within our planet to escape.
Earth, however, did not lose all of its helium-3 at that time. It still contains some of the rare gas that seeps out of Earth's interior. The core would be an ideal location for such a reservoir because it is "less sensitive to big impacts than other regions of the Earth system," according to the researchers, and it is not affected by tectonic plate cycling, which releases helium gas.
The researchers are hoping to discover more evidence to back up their results. Finding additional nebula-created gases, such as hydrogen, escaping from Earth in identical locations and at similar rates as helium-3, for example, might be a "smoking gun" indicating that the core is the source.
"There are many more mysteries than certainties," Olson said.
