Ancient helium leaking from core offers clues to Earth's formation
Vast stores of helium from the Big Bang lingering in the core suggest
Earth formed inside a solar nebula
Date:
March 28, 2022
Source:
American Geophysical Union
Summary:
Helium-3, a rare isotope of helium gas, is leaking out of Earth's
core, a new study reports. Because almost all helium-3 is from
the Big Bang, the gas leak adds evidence that Earth formed inside
a solar nebula, which has long been debated.
FULL STORY ========================================================================== Helium-3, a rare isotope of helium gas, is leaking out of Earth's core,
a new study reports. Because almost all helium-3 is from the Big Bang,
the gas leak adds evidence that Earth formed inside a solar nebula,
which has long been debated.
========================================================================== Helium-3 has been measured at Earth's surface in relatively small
quantities.
But scientists did not know how much was leaking from the Earth's core,
as opposed to its middle layers, called the mantle.
The new study pins down the core as a major source of helium-3 for
the Earth.
Some natural processes can generate helium-3, such as the radioactive
decay of tritium, but helium-3 is made primarily in solar nebulae --
massive, spinning clouds of gas and dust like the one that gave rise to
our Solar System. Because helium is one of the earliest elements produced
in the universe, most helium- 3 can be traced back to the Big Bang.
As a planet grows, it accumulates material from its surroundings, so its composition reflects the environment in which it formed. To get high concentrations of helium-3 deep in the core, Earth would have had to
form inside a thriving solar nebula, not on its fringes or during its
waning phase.
The new research adds further clues to the mystery surrounding Earth's formation, lending additional evidence to the theory that our planet
formed inside the solar nebula.
The study was published in the AGU journal Geochemistry, Geophysics, Geosystems, which publishes research on the chemistry, physics, geology
and biology of Earth and planetary processes.
About 2,000 grams of helium-3 leak out of the Earth every year, "about
enough to fill a balloon the size of your desk," said lead study author
Peter Olson, a geophysicist at the University of New Mexico. "It's 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."
The researchers modeled helium during two key stages of Earth's history:
early formation, when the planet was accumulating helium, and following
the formation of the Moon, after which helium was lost. Evidence
suggests an object one-third the size of the Earth hit the planet early
in its history, around 4 billion years ago and that impact would have
re-melted the Earth's crust, allowing much of the helium to escape. The
gas continues escaping to this day.
Using the modern helium-3 leak rate along with models of helium isotope behavior, the researchers estimated there are between 10 teragrams
(1013 grams) to a petagram (1015 grams) of helium-3 in the core --
a vast quantity that Olson said points to Earth's formation inside the
solar nebula, where high concentrations of the gas would have allowed
it to build up deep in the planet.
However, future work looking for other nebula-created gases, such as
hydrogen, leaking in similar rates and locations as helium-3 could be a "smoking gun" for the core as the source, Olson said. "There are many
more mysteries than certainties."
========================================================================== Story Source: Materials provided by American_Geophysical_Union. Note:
Content may be edited for style and length.
========================================================================== Journal Reference:
1. 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 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/03/220328133609.htm
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