Earth’s core is losing helium-3 at a rate of around 2,000 grams per year , scientists have found. Although some natural processes can produce helium-3, this isotope of helium gas is created primarily in nebulae, and most dates back to the Big Bang. It is believed that it arrived on our planet when a body similar to Mars collided with Earth 4,533 million years ago.
Almost all helium-3 comes from the Big Bang
The peculiar isotope that formed during the Big Bang is therefore escaping, seeping out of the Earth’s core, and giving us a key clue about how our planet came to be.
While most of the helium found on Earth exists as helium-4 (differs in mass from helium-3 by one neutron), small amounts of helium-3 have been detected in volcanic rocks known as oceanic island basalts. (OIB). Some natural processes such as the radioactive decay of tritium can generate helium-3, but helium-3 is produced mainly in solar nebulae: massive clouds of gas and dust that rotate like the one that gave rise to our solar system.
Why is this ancient helium leaking out of the core?
Scientists do not know it, but their finding indicates that our own Earth would have formed even earlier than previously thought. The fact that the Earth has this helium-3 so early in the history of our solar system indicates new clues about the origin of our planet. In fact, the big reveal of this finding, of this gas leak from the cosmic dawn, is that it shakes up the current paradigm about how closely our Earth formed relative to our young Sun.
“It is a wonder of nature , and a clue to Earth’s history, that there is still a significant amount of this isotope in the Earth’s interior,” say the authors of the study published in the journal Geochemistry, Geophysics, Geosystems.
Evidence suggests that an object a third the size of Earth hit the planet early in its history, and that impact would have re-melted the Earth’s crust, allowing much of the helium to escape. And the gas continues to leak to this day.
The new work carried out by researchers at the University of New Mexico shows that this rare isotope of helium gas was formed during the Big Bang and then gradually incorporated into the Earth’s core as our planet formed, inside a nebula solar.
In this way, the worlds would have formed rapidly in the presence of the solar nebula; small pebble-sized chunks would have hurtled toward the Sun from all corners of the solar system, and as the protoplanets revolved around the sun, they would have picked up these pebbles and accumulated their mass rapidly, in just about two million years, while the nebula still existed, instead of several million years after it had vanished.
Several uncertainties remain
Despite this theory suggesting that the planet must have formed within a thriving solar nebula, the probability that the conditions for helium-3 sequestration in the Earth’s core are met is moderately low , meaning that there might be less isotope of helium-3 than this study suggests.
The authors hope to confirm this theory by detecting other gases created by nebulae escaping from the center of the Earth. But, for now, we have more mysteries than certainties. For example , why does helium-3 come out of the interior of the Earth, after 4.56 billion years of history?
What we discover from now on will also be relevant to explorations of stars and exoplanets in other parts of the universe.
Referencia: Peter L. Olson, Zachary D. Sharp. Primordial Helium‐3 Exchange Between Earth’s Core and Mantle. Geochemistry, Geophysics, Geosystems, 2022; 23 (3) DOI: 10.1029/2021GC009985
