Scientists Uncover the Mystery of Earth’s Inner Water Dynamics

Depiction: Silica crystals emerge from Earth’s outer core’s liquid metal due to a water-induced chemical reaction. Credit: Dan Shim/ASU

A recent pivotal study suggests that water from Earth’s surface extends to its core, changing its chemical makeup. This indicates a more intricate core-mantle interaction and an elaborate global water cycle.

Historically, a mysterious thin layer deep within the Earth, named the E prime layer, was identified by seismologists. Its origins have been unclear until now.

An international research team, including members from Arizona State University’s School of Earth and Space Exploration such as Dan Shim, Taehyun Kim, and Joseph O’Rourke, discovered that water from Earth’s surface deeply penetrates the planet. This alters the composition of the outer core’s metallic liquid, forming a distinct, thin layer.

The team’s findings were published on November 13 in Nature Geoscience.

Deep Water Movement Process

Studies indicate that over eons, surface water has been carried deep into Earth by descending tectonic plates. At the core-mantle boundary, nearly 1,800 miles below the surface, this water initiates a significant chemical reaction, modifying the core’s structure.

Depiction: Earth’s internal structure showing subducting water and ascending magma plume. At the core-water interface, a chemical reaction creates a hydrogen-rich layer in the outer core’s top and dense silica at the mantle’s bottom. Credit: Yonsei University

Chemical Dynamics at the Core-Mantle Boundary

Yong Jae Lee of Yonsei University and Shim’s group conducted high-pressure experiments showing that subducted water chemically interacts with core materials. This results in a hydrogen-rich, silicon-depleted layer, transforming the outer core’s top region into a film-like structure. Moreover, this reaction produces silica crystals that ascend into the mantle. This newly formed liquid metallic layer is presumed to be lighter and have slower seismic velocities, correlating with the unusual properties identified by seismologists.

Core-Mantle Exchange and Global Effects

“For a long time, it was thought that the core-mantle material exchange was minimal. However, our recent high-pressure experiments suggest otherwise. We observed that water interacting with silicon at the core-mantle boundary forms silica,” explained Shim. “Coupled with our earlier findings of diamonds created from water reacting with carbon in iron liquid under high pressure, this points to a more active core-mantle exchange, indicating significant material transfer.”

This breakthrough enhances our comprehension of Earth’s internal mechanisms, suggesting a broader global water cycle than previously thought. The core’s altered ‘film’ has significant implications for the geochemical cycles linking the surface water cycle with the deep metallic core.

Reference: “A hydrogen-enriched layer in the topmost outer core sourced from deeply subducted water” by Taehyun Kim, Joseph G. O’Rourke, Jeongmin Lee, Stella Chariton, Vitali Prakapenka, Rachel J. Husband, Nico Giordano, Hanns-Peter Liermann, Sang-Heon Shim, and Yongjae Lee, 13 November 2023, Nature Geoscience.
DOI: 10.1038/s41561-023-01324-x

The research was performed by a global team of geoscientists using advanced methods at the Advanced Photon Source of Argonne National Lab and PETRA III of Deutsches Elektronen-Synchrotron in Germany, replicating the extreme conditions at the core-mantle boundary.

The project involved ASU’s Kim, initially a visiting PhD student now a postdoctoral researcher; Shim, a leading professor who conducted the high-pressure experiments; and O’Rourke, an assistant professor performing computational simulations. Lee led the Yonsei University team, with key researchers Vitali Prakapenka, Stella Chariton, Rachel Husband, Nico Giordano, and Hanns-Peter Liermann.

This work received support from the NSF Earth Science program.

Frequently Asked Questions (FAQs) about Earth’s water cycle

More about Earth’s water cycle

• Nature Geoscience Study on Earth’s Water Dynamics
• Arizona State University School of Earth and Space Exploration
• Yonsei University Research Publications
• Advanced Photon Source at Argonne National Lab
• Deutsches Elektronen-Synchrotron Research
• NSF Earth Science Program