How scientists revealed the secrets of Earth’s deep waters

Illustration of silica crystals emerging from the liquid metal in the Earth’s outer core as a result of a chemical reaction resulting from water. Credit: Dan Shim/Arizona State University

A pioneering study reveals that Earth’s surface water reaches the core, changing its composition and suggesting a more dynamic interaction between the core and mantle and a complex global water cycle.

A few decades ago, seismologists imaging the deep planet identified a thin layer just over a few hundred kilometers thick. The origin of this layer, known as primary layer E, has until now been a mystery.

An international team of researchers, including Arizona State University scientists Dan Shim, Taehyun Kim, and Joseph O’Rourke from the College of Earth and Space Exploration, has revealed that water from Earth’s surface can penetrate deep into the planet, changing the planet’s composition. The outer region of the liquid metal nucleates and forms a characteristic thin layer.

Their research was published November 13 in the journal Natural earth sciences.

Deep water transportation process

Research indicates that over billions of years, surface water has been transported deep into the Earth by subducting or subducting tectonic plates. Reaching the boundary between the core and mantle, about 1,800 miles below the surface, this water triggers a deep chemical reaction, changing the structure of the core.

Illustration of Earth’s interior revealing subducting water and a rising column of magma. At the interface where embedded water meets the core, chemical exchange occurs to form a hydrogen-rich layer in the upper outer core and dense silica at the bottom of the mantle. Credit: Yonsei University

Chemical reactions at the core-mantle boundary

Along with Young Jae Lee from Yonsei University In South Korea, Shim and his team demonstrated through high-pressure experiments that submerged water chemically reacts with underlying materials. This reaction forms a hydrogen-rich, silicon-depleted layer, changing the upper outer core region into a film-like structure. In addition, the reaction generates silica crystals that rise and fuse into the mantle. This modified liquid mineral layer is expected to be less dense, with lower seismic velocities, consistent with the anomalous characteristics mapped by seismologists.

Core-mantle interaction and global effects

“For many years, the physical exchange between the Earth’s core and its mantle was thought to be small. However, our recent high-pressure experiments reveal a different story. “We found that when water reaches the boundary between the core and the mantle, it interacts with the silicon in the core,” Shim said. , forming silica.” “This discovery, along with our previous observation of diamonds forming from the reaction of water with carbon in liquid iron under extreme pressure, indicates a much more dynamic interaction between the core and the mantle, indicating a significant physical exchange.”

This discovery advances our understanding of Earth’s internal processes, suggesting a more extensive global water cycle than previously recognized. The changing “layer” of the core has profound implications for the geochemical cycles linking the surface water cycle to the deep mineral core.

Reference: “A hydrogen-rich layer in the upper outer core originates from deeply submerged water” by Taehyun Kim, Joseph J. O’Rourke, Jeongmin Lee, Stella Chariton, Vitaly Prakapinka, Rachel J. Husband, Nico Giordano, Hans-Peter Lerman, Sang-Hyun Shim, and Youngjae Lee, 13 November 2023, Natural earth sciences.
doi: 10.1038/s41561-023-01324-x

The study was conducted by an international team of geoscientists using advanced experimental techniques at the Advanced Photon Source at Argonne National Laboratory and PETRA III from Deutsches Elektronen-Synchrotron in Germany to replicate the extreme conditions at the core-mantle boundary.

Team members and their key roles from ASU are Kim, who began this project as a visiting doctoral student and is now a postdoctoral researcher in the School of Earth and Space Exploration; Wasim, a professor at the School of Earth and Space Exploration, who led the high-pressure experimental work; O’Rourke, an assistant professor in the School of Earth and Space Exploration, ran computational simulations to understand the formation and continuity of the changing thin layer in the core. Lee led the research team from Yonsei University, along with principal research scientists Vitaly Prakapinka and Stella Chariton at the Advanced Photon Source and Rachel Zug, Nico Giordano and Hans-Peter Lerman at the Deutsches Elektronen-Synchrotron.

This work was supported by the NSF Earth Sciences Program.