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A few decades ago, seismologists mapping the deep planet identified a thin layer just over a few hundred kilometers thick. The origin of this layer, known as the E-prime layer, has been a mystery until now.
An international team of researchers, including scientists Dan Shim, Taehyun Kim and Joseph O’Rourke from Arizona State University’s School of Earth and Space Exploration, has revealed that water from Earth’s surface can penetrate deep into the planet and change the composition of the earth can change. outer region of the metal liquid core and creates a clear, thin layer. Illustration of silica crystals emerging from the liquid metal of the Earth’s outer core as a result of a water-induced chemical reaction.
Their research was recently published in Nature Geoscience.
Research shows that surface water has been transported deep into the Earth over billions of years by descending or subducting tectonic plates. Upon reaching the core-mantle boundary, about 3,000 kilometers below the surface, this water causes a profound chemical interaction, changing the structure of the core.
Together with Yong Jae Lee of Yonsei University in South Korea, Shim and his team have shown through high-pressure experiments that submerged water chemically reacts with nuclear materials. This reaction forms a hydrogen-rich, silicon-poor layer, turning the upper outer core region into a film-like structure. Furthermore, the reaction generates silica crystals that rise and integrate into the mantle. This modified liquid metal layer is predicted to be less dense, with lower seismic velocities, consistent with anomalous features mapped by seismologists.
Illustration of the interior of the Earth, where sinking water and a rising plume of magma are visible. At the interface where sinking water meets the core, a chemical exchange takes place, creating a hydrogen-rich layer in the upper outer core and dense silica at the bottom of the mantle. Image courtesy of Yonsei University
‘For years it was assumed that the material exchange between the Earth’s core and mantle is small. Yet our recent high-pressure experiments reveal a different story. We discovered that when water reaches the core-mantle boundary, it reacts with silicon in the core. core, creating silica,” said Shim. “This discovery, together with our previous observation of diamonds forming from water reacting with carbon in iron fluid under extreme pressure, points to a much more dynamic core-mantle interaction, indicating on substantial material exchange.”
This finding expands our understanding of Earth’s internal processes and suggests a more extensive global water cycle than previously recognized. The altered ‘film’ of the core has profound consequences for the geochemical cycles that connect the surface water cycle to the deep metallic core.
This study was conducted by an international team of geoscientists using advanced experimental techniques at the Advanced Photon Source at Argonne National Lab and PETRA III at Deutsches Elektronen-Synchrotron in Germany to replicate the extreme conditions at the core-mantle boundary.
Members of the team and their key roles at ASU include Kim, who began this project as a visiting PhD candidate and is now a postdoctoral researcher in the School of Earth and Space Exploration; Shim, a professor at the School of Earth and Space Exploration, who led the high-pressure experimental work; and O’Rourke, an assistant professor in the School of Earth and Space Exploration, who performed computational simulations to understand the formation and persistence of the core’s altered thin layer. Lee led the research team from Yonsei University, along with key research scientists Vitali Prakapenka and Stella Chariton at the Advanced Photon Source and Rachel Husband, Nico Giordano and Hanns-Peter Liermann at the Deutsches Elektronen-Synchrotron.
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