(ORDO NEWS) — Ancient helium from the Big Bang is leaking out of the Earth’s core, scientists report in a new study.
There is no reason to be alarmed. The earth doesn’t deflate like a balloon. What this actually means is that the Earth formed inside the solar nebula the molecular cloud that gave birth to the Sun a detail about the birth of our planet that has long remained unresolved.
It also suggests that other primordial gases may leak from the Earth’s core into the mantle, which in turn could provide information about the composition of the solar nebula.
Helium on Earth is represented by two stable isotopes. By far the most common is helium-4, with a nucleus containing two protons and two neutrons. Helium-4 makes up about 99.99986% of all helium on our planet.
Another stable isotope, which makes up about 0.000137% of Earth’s helium, is helium-3, with two protons and one neutron.
Helium-4 is primarily a product of the radioactive decay of uranium and thorium, produced right here on Earth. In contrast, helium-3 is mostly primordial, formed immediately after the Big Bang, but it can also be produced from the radioactive decay of tritium.
The helium-3 isotope has been found to be escaping from the Earth’s interior, mostly along the mid-ocean volcanic ridge system, which gives us a pretty good idea of the rate at which it leaves the crust.
The rate is about 2,000 grams per year: “enough to fill a balloon the size of your desk,” explains geophysicist Peter Olson of the University of New Mexico.
“It’s a miracle of nature and a clue to Earth’s history that there is still a significant amount of this isotope in the Earth’s interior.”
What is less clear is the origin; how much helium-3 can exit the core compared to how much is in the mantle.
This will tell us the source of the isotope. When the Earth formed, it accumulated material from the dust and gas floating around the newborn Sun.
The only way that a significant amount of helium-3 could be inside the planetary core is if it formed in a booming nebula. So, not on its outskirts, and not in the way it scattered and deflated.
Olson and his colleague, geochemist Zachary Sharp of the University of New Mexico, conducted the study by simulating the Earth’s supply of helium as it evolved. First, the process of formation of a protoplanet, during which it accumulated and included helium; and then after the Great Impact.
Astronomers believe this happened when a Mars-sized object crashed into a very young Earth, sending debris into Earth’s orbit that eventually recombined to form the Moon.
During this event, which would have resulted in the re-melting of the mantle, much of the helium contained within the mantle would have been lost. The core, however, is more impact resistant, suggesting that it could be a very efficient reservoir for holding helium-3.
In fact, this is what the researchers found. Using the current rate of helium-3 leakage from the inside, as well as models of the behavior of the helium isotope, Olson and Sharp found that it is likely that 10 teragrams (1013 grams) per petagram (1015 grams) of helium-3 into the core of our planet.
This suggests that the planet must have formed inside a thriving solar nebula. However, several uncertainties remain. The probability of meeting all conditions for helium-3 sequestration in the Earth’s core is moderately low, meaning that there may be less isotope than the team’s work suggests.
However, it is possible that there is also abundant primordial hydrogen in the core of our planet, involved in the same process that could accumulate helium-3. Searching for evidence of a hydrogen leak could help confirm the findings, the researchers said.
Contact us: [email protected]