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Scientists have detected an unexpected ratio of helium-4 and helium-3, an ultra-rare element with futuristic potential applications, in Arctic rocks that may have originated in Earth’s core. The discovery sheds new light on the deepest and most mysterious region of our planet, and hints that helium-3 from the core might escape upward through the mantle and eventually erupt on the surface as a part of lava flows.
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Helium-3 is an isotope, or version, of helium that has only one neutron instead of two. It is considered to be a promising fuel for nuclear fusion reactions, a speculative energy source based on the same processes that power the Sun and other stars. Helium-3 is also a primordial ingredient of our planet that could illuminate key processes in the core, such as the generation of Earth’s protective magnetic field, which has played a major role in the emergence of life on Earth. Most helium-3 in the universe dates nearly all the way back to the Big Bang 13.8 billion years ago, distinguishing it as an incredibly ancient gas that often hangs around in nebulas. When Earth began to form some 4.6 billion years ago, helium-3 from the solar nebula became trapped in its core, where it remains with other primordial elements to this day. Previous research has suggested that trace amounts of this rare element may leech out of the core and travel up to Earth’s surface, but the finer details of this hypothesis are still a mystery.Now, scientists led by Forrest Horton, a geochemist at Woods Hole Oceanographic Institution, have discovered that ancient lava flows from Baffin Island, a huge landmass in Canada’s Arctic Archipelago, contain the highest ratios of helium-3 (3He) to helium-4 (4He), another isotope, ever seen in any terrestrial volcanic rocks. The team suggests that “the extremely high 3He/4He helium in these lavas might derive from Earth’s core,” a finding that may rewrite the history of ancient elements in the center of our world, according to a study published on Wednesday in Nature.
“The high 3He/4He in these lavas make them especially important for understanding Earth's formation and its deep interior,” Horton told Motherboard in an email. “Because most of the 3He in lavas globally was presumably trapped in Earth during planetary formation, rocks with especially high relative abundances of 3He provide clues about planetary accretion and subsequent evolution. This was the motivation for reassessing the Baffin Island lavas.”“Also, the location is very remote and on lands that are treasured by the Inuit, so access is restricted compared to places like Hawaii,” he continued. “We worked with local organizations and the Canadian National Park Service, both of which provided essential support. We also had to stage a helicopter there to gain access.”Though scientists were already aware that Baffin Island’s rocks contain helium-3, Horton and his colleagues took this research to the next level by comparing and duplicating measurements of helium-3 and helium-4 in olivine rock from multiple lava flows in the region. The team reported that the “highest 3 He/4 He values we measured” were “significantly higher than previously reported in igneous rocks on Baffin Island or elsewhere,” according to the study.“Previous studies found that this suite of lavas on Baffin Island had higher magmatic 3He/4He than has been identified elsewhere on Earth. So, finding high 3He/4He in these rocks was not unexpected,” Horton said. “What was surprising was that we measured 3He/4He ratios that extend to much higher values than previously thought.”
“A high 3He/4He ratio means that there is more 3He relative to 4He compared to other rocks,” he explained. “However, 3He is very scarce compared to 4He, even in these rocks. For instance, there is only about one 3He atom per million 4He atoms. But because helium is a noble gas (i.e., it does not chemically react with other elements) and because so little helium exists in our atmosphere (consequently, we don't have to worry very much about contamination), we can measure the 3He/4He ratio very precisely.”These updated readings of Baffin Island’s helium isotopes support the idea that small amounts of helium-3, along with other elements, are leaking out of the core. After they escape, these elements could become incorporated into subterranean structures called mantle plumes that shape some of Earth’s most spectacular volcanic hotspots, like those in modern Hawaii and Iceland, or Baffin Island in the past. This primordial helium-3 may contain secrets about the formation of our planet that cannot be accessed in other ways.“We know very little about Earth's core, other than that it exists,” Horton said. “This makes studying the core both intriguing and frustrating. Traditionally, the core and outer layers of our planet (mantle and crust) were presumed to be geochemically isolated (i.e., material does not transfer back and forth). Increasingly, scientists have been challenging this notion.”
“I think that our work lends credence to the idea that material, or at least helium, leaks out of the core,” he continued. “I find this exciting because it suggests that the deep Earth is more dynamic than we realized: elements move between the metallic and rocky parts of our planet. Also, helium in the core may have survived the Moon-forming giant impact, which is believed to have melted and mixed all of the rocky material on Earth. So, the high 3He/4He ratios we measured may be an indication that helium—and perhaps other light elements like hydrogen and carbon—survived the cataclysmic origins of our planet by being sheltered in the core.”In other words, Earth’s core is a treasure trove of weird ancient elements that were locked away so tightly billions of years ago that even the epic planetary collision that formed the Moon could not shake them loose. But while traces of this primordial helium-3 may turn up in special places on Earth, like Baffin Island, we would need to seek more abundant sources of this resource for potential extraction toward technological applications, such as nuclear fusion.
“3He is exceptionally rare in Earth because helium that is released from the solid Earth escapes to space, and because little 3He is produced within our planet (unlike 4He, which is the product of radioactive decay of naturally occurring isotopes),” Horton said. “Our study may contribute to our understanding of the origins of terrestrial 3He but does not guide efforts to extract 3He from rocks or produce energy from 3He.” “Note that cosmic ray bombardment enriches 3He in the top few meters of rocky bodies in the Solar System, so ancient surfaces like those on the Moon and meteorites can have much higher 3He/4He than observed in the Baffin Island lavas,” he added.Perhaps one day, helium-3 will become valuable enough as a potential resource to motivate prospectors to mine it on other worlds, a scenario that has been explored in many science fiction stories, such as the film Moon. In the meantime, scientists like Horton are eager to understand the origin and implications of Earth’s ultra-scarce helium-3 reserves, which could offer an entirely new view of the mysterious core 1,800 miles under our feet.
“In many ways, our study raises more questions than it answers, so there is a lot of work to do,” Horton said. “One important question is, assuming helium is leaking out of the core, whether any other elements also escape from the core? And when did these elements migrate into the rocky part of the planet?” “I am especially excited to explore potential links between helium and other elements, including hydrogen and carbon (essential building blocks of life),” he concluded. “Another implication of our study is that mantle plumes that deliver material from the deep Earth evolve over time; a systematic study of mantle plume evolution may provide a clearer picture of processes near the core-mantle boundary.”Update: A previous version of this article had the headline “Earth’s Core Is Leaking In the Arctic and Scientists Don’t Know Why.” Lead author Forrest Horton expressed to Motherboard that the leak occurred far below the surface of the Earth and ended up in surface lava via mantle plumes. Motherboard has updated the headline to reflect this.