Researchers at the University of Science and Technology of China have found that Earth’s core may be steadily leaking hydrogen, helium, and tungsten up into the mantle. Using machine learning simulations published in Science Advances, the study overturns long-held geological models about our planet’s early formation.
Our early Earth was a punishing environment, forged from a global magma ocean and pelted by debris while blazing as hotly as the surface of the Sun. Over 4.5 billion years of cosmo-geological time, dense heavy elements sank to form the core while lighter materials settled into the mantle and crust. Standard geological models long taught that these inner layers remained neatly separated, with primordial matter locked securely away since the planet’s birth.
That textbook view is now shifting. Throughout the planet’s extended development, researchers at the University of Science and Technology of China in Hefei concluded that Earth’s core may have transferred materials to the strata situated above it. Rather than sitting as static relics from the planet’s genesis, deep-mantle chemical markers reflect dynamic modification by ongoing core-mantle exchange throughout Earth’s evolution, according to the researchers.
Machine-Learning Simulations Track Hydrogen Isotopes
To investigate how elements migrate across the deep boundary, the team turned to advanced computing. They used computer simulations enhanced by machine learning to analyze the quantum action of molecules and atoms. Hydrogen proved especially critical because its low atomic mass makes its isotopic composition exceptionally sensitive to internal temperatures and pressures.
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By tracking the ratio of regular hydrogen to deuterium—a heavier isotopic variant—the geoscientists modeled the crystallization of the primordial magma ocean. Their calculations demonstrated that mineral-melt fractionation was weak, meaning the ancient mantle should have acquired a remarkably uniform hydrogen isotope makeup regardless of wide fluctuations in temperature and pressure. The starting hydrogen isotope composition of the magma ocean mattered far more than its initial water content.
This upward migration of hydrogen from the core supplies the mantle with fresh material and depresses its D/H proportion. This process brings up light hydrogen that originally accumulated from the giant cloud of gas and dust that formed the Sun.
Volcanic Rocks on Baffin Island and in Iceland Reveal Primordial Traces
Physical evidence of this deep-earth leaking surfaces through ocean island basalts. These volcanic rocks form when hot material rises in upwelling plumes from near the boundary separating the core and the mantle.
Such rocks are recovered from locations including Baffin Island, located in Nunavut, Canada, and from Iceland, located in Iceland. These eruptions carry chemical signatures acting as a geochemical time capsule from the solar nebula that predates our solar system.
Helium and tungsten provide additional markers confirming the exchange. Primordial helium-3, which originated from the birth of the solar system, pairs with heavier helium-4 produced continuously by radioactive decay in Earth’s upper layers. Meanwhile, heavy tungsten was sequestered in the core during planetary crystallization, but ancient tungsten isotopes now hitch rides on rising plumes to trace core materials moving upward.
Implications for Deep Mantle Reservoirs
The findings challenge the assumption that chemical signatures in the deep Earth are simple leftovers from planetary cooling.
These findings suggest that even if primordial deep-mantle reservoirs once existed, the hydrogen isotope signatures in the present-day deep lower mantle are unlikely to represent simple relics of early differentiation.
Researchers, Science Advances