A recent modelling research reveals that an exceptionally rare form of helium that was produced just after the Big Bang is seeping out of Earth’s iron core.
The great bulk of this gas in the cosmos, known as helium-3, is primordial and was generated shortly 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 enormous, whirling, and collapsing cloud assumed to have contributed to the formation of the solar system.
The revelation that Earth’s core likely includes a massive pool of helium-3 adds to the evidence that Earth formed amid a thriving solar nebula, not on its outskirts or during its waning phase, according to the researchers.
Peter Olson, a geophysicist at the University of New Mexico who also acted as the lead author of this research stated that Helium-3 is “a miracle of nature, and a hint for the history of the Earth, that there’s still a considerable quantity of this isotope in the interior of the Earth.”
Helium-3 is an isotope, or variation, of helium with one neutron instead of the typical two in its nucleus. It is a rare gas, accounting for only 0.0001% of all helium on Earth. It is produced by a number of processes, including the radioactive decay of tritium, a rare radioactive isotope of hydrogen. However, because helium was one of the first elements to exist in the cosmos, the majority of helium-3 most likely originated with the Big Bang.
Scientists already knew that about 4.4 pounds (2 kilograms) of helium-3 escapes from Earth’s interior each year, mostly along the mid-ocean ridge system where tectonic plates meet, the researchers wrote in the study, which was published online March 28 in the journal Geochemistry, Geophysics, Geosystems. According to the lead researcher, Olson, this amount of gas is enough to inflate a balloon the size of a desk.
However, scientists were unsure how much helium-3 originated from the core versus the mantle, and how much helium-3 existed in Earth’s reservoirs.
Traverse of Helium
To explore, the researchers modelled helium abundance at 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 lot of this gas. Scientists believe the moon originated around 4 billion years ago when a massive asteroid the size of Mars crashed with Earth.
This catastrophe would have burned Earth’s crust, allowing most of the helium inside our planet to escape.
However, Earth did not lose all of its helium-3 at that time. It still contains some of the rare gas, which continues to leak from the Earth’s interior. The core would be an excellent location for such a reservoir “because it is less sensitive to significant impacts compared to other sections of the Earth system,” the researchers stated in the report, and it is not involved in tectonic plate cycling, which also releases helium gas.
The researchers combined modern helium-3 leak rates with simulations of helium isotope dynamics. These calculations found that between 22 billion pounds (10 tera-grams) and 2 trillion pounds (1 pentagram) of helium-3 are present in Earth’s core – a tremendous quantity, indicating that Earth originated in a solar nebula with large quantities of the gas.
Their gas-exchange models “Exchange throughout Earth’s origin and development implicate the metallic core as a leaky reservoir that provides helium-3 to the rest of the Earth,” the researchers said in the report.
However, because these conclusions are based on modelling, they are not without flaws. The scientists had to make a variety of assumptions, such as that Earth took in helium-3 when it formed in the solar nebula, that helium entered core-forming metals, and that some helium departed the core for the mantle. These assumptions, together with other uncertainties, such as how long the solar nebula lasted relative to the rate at which Earth formed, suggest that there may be less helium-3 in the core than the scientists predicted.
However, the researchers are hoping to uncover additional evidence to back up their results. Finding additional nebula-created gases, such as hydrogen, escaping off Earth from comparable locations and at similar rates as helium-3, for example, may be a “smoking gun” indicating that the core is the source, Olson said. “There are much more unknowns than certainties.”
Published By :- Tarsem Singh
Edited By :- Khushi Thakur