Scientists have discovered that the helium trapped in the core during the formation of the Earth is slowly making its way to the surface
Record concentrations of a helium isotope found within 62-million-year-old Arctic rocks may be the most compelling evidence to date of a slow leak occurring in our planet’s core. Based on the results of a previous analysis, a team of California geochemists are certain that helium trapped in the core during the formation of our planet is making its way to the surface.
Because there are leaks of helium from the Earth’s core
Being so light and non-reactive, there is little to stop helium from diffusing off rocks and into space. This makes it a material incredibly rare on the surface of our planet. Yet, why this element remains trapped deep beneath our feet is one of geology’s great unknowns. After about 4.6 billion years, most of the helium ingested by Earth in the past should have already been expelled. Any traces of gas found in volcanic rock deposits would have to come from mantle pockets that have yet to expel their helium, or from a slow-leaking reservoir.
The concentration of helium inside the planet
The basaltic lavas of Canada’s Baffin Island contain some of the world’s highest ratios of helium 3 (3 He) to the slightly heavier isotope, helium 4 (4 He). For geologists, such a mixture indicates that the presence of the gas is not contamination from the atmosphere, but rather a sign of deeper, more ancient origins. Several years ago, Woods Hole Oceanographic Institution geochemist Forrest Horton discovered helium isotope ratios up to 50 times higher than atmospheric levels in olivine samples collected from Baffin lava fields, making them elevated.
What scientists concluded
This unusual concentration of 3 He was also present in the lavas of Iceland. Without ruling out the possibility of coincidence, Horton and his team wondered whether both hotspots might have received helium from an ancient reservoir adjacent to the mantle. Now it seems that their intuition may be correct. , which includes a collection of olivine taken from dozens of sites on Earth, provided the highest ratio of 3 He to 4 He ever recorded in volcanic rock, measuring nearly 70 times anything seen in the atmosphere. Also taking into account the ratios of other isotopes, including strontium and neodymiumthe team was able to rule out factors that might have altered the identity of the helium after the eruption, building an even stronger case for the gas’s unusual origins.
The most inaccessible place on Earth
Tracing neon and helium to the core is not as complicated as it might seem at first glance. Simulations of the thermodynamics, pressures and composition of the bowels of our planet suggest that reserves of noble gases trapped in the core could have penetrated the mantle over time, until they slowly emerged to the surface. Hidden behind thousands of kilometers of dense, hot rock, the Earth’s core is inaccessible. Our only way to study it is to listen carefully to the way our planet echoes beneath its skin. If it were to escape, we might have another way to study its processes and learn a lot about how planets like ours sprang from a swirl of primordial dust and gas.
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