An extremely rare type of helium that was created shortly after the Big Bang is escaping from Earth’s metallic core, according to a new modeling study.
The vast majority of this gas in the universe, called helium-3, is primordial and was created right after the big Bang occurred about 13.8 billion years ago. Some of this helium-3 would have joined other particles of gas and dust in the solar nebula – the large, spinning, collapsing cloud that would have led to the creation of the solar system.
The discovery that Earth’s core likely contains a vast reservoir of helium-3 is further evidence supporting the idea that Earth formed inside a blooming solar nebula, not at its periphery or during its decline phase, the researchers said.
Helium-3 is “a wonder of nature, and a clue to the history of Earththat there is still a significant amount of this isotope inside the Earth,” said the study’s lead author, Peter Olson, a geophysicist at the University of New Mexico, said in a press release.
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Helium-3 is an isotope, or variant, of helium that has one neutron instead of the usual two in its nucleus. It is a rare gas, which represents only 0.0001% of helium on Earth. It comes from various processes, such as the radioactive decay of tritium, a rare radioactive isotope of hydrogen. But because helium is one of the first elements to exist in the universe, most helium-3 probably comes from 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, published online March 28 in the journal Geochemistry, Geophysics, Geosystems.
That’s “about enough to fill a balloon the size of your desk,” Olson said.
But scientists didn’t know exactly how much helium-3 came from the core versus the mantle, and how much helium-3 was in Earth’s reservoirs.
To investigate, the research team modeled the abundance of helium during two important phases of Earth’s history: the planet’s early formation, when it was still accumulating helium, and after the formation of the moon, when our planet lost a lot of this gas. Scientists believe the moon formed when a colossal Mars-sized object collided with Earth around 4 billion years ago.
This event would have melted the earth’s crust and allowed much of the helium inside our planet to escape.
However, the Earth did not lose all of its helium-3 at this time. It still retains some of the rare gas, which continues to seep from the bowels of the Earth. The core would be a good location for such a reservoir, “because it is less vulnerable to large impacts than other parts of the Earth system,” the researchers wrote in the study, and it is not involved in the cycling of tectonic plates, which also gives off helium gas.
The researchers coupled the modern helium-3 leak rate with models of helium isotope behavior. These calculations revealed that between 22 billion pounds (10 teragrams) and 2 trillion pounds (1 pentagram) of helium-3 is lying around in the Earth’s core – a huge amount, indicating that the Earth formed in a solar nebula with high concentrations of gas.
Their models of gas exchange “during Earth’s formation and evolution implicate the metallic core as a leaky reservoir that supplies the rest of the Earth with helium-3,” the researchers wrote in the study. .
However, as these results are based on modeling, the results are not foolproof. The team had to make a number of assumptions – for example that the Earth took up helium-3 when it formed in the solar nebula, that helium entered the metals forming the core and that some of the helium has left the core for the mantle. These assumptions, in addition to other uncertainties, including the lifespan of the solar nebula relative to the rate at which Earth formed, mean there could be less helium-3 in the core. than they calculated, the scientists said.
But the researchers hope to find more clues that support their findings. For example, finding other nebula-created gases, such as hydrogen, leaking from Earth from similar locations and at similar rates to helium-3 could be a “smoking gun.” showing that the kernel is the source, Olson said. “There are far more mysteries than certainties.”
Originally posted on Live Science.