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Surface water can penetrate deep into Earth's core

An international team of scientists have unveiled a significant interaction between Earth’s surface water and its deep interior. The study challenges previous ideas about the dynamics between the Earth’s core and mantle. 

E prime layer 

The research sheds light on the mysterious E prime layer – a thin, enigmatic zone located at the core-mantle boundary.

A few decades ago, seismologists imaging deep beneath the Earth’s surface identified this thin layer, just over a few hundred kilometers thick. The origin of the E prime layer, however, remained elusive until now. 

The research team included Dan Shim, Taehyun Kim, and Joseph O’Rourke of Arizona State University, as well as Yong Jae Lee of Yonsei University in South Korea.

Transformative journey

The scientists have discovered that surface water can penetrate deep into the planet. This process significantly alters the composition of the outermost region of the metallic liquid core, forming a distinct, thin layer.

The researchers have shown that over billions of years, surface water is transported into the Earth’s deep interior by subducting tectonic plates. 

Chemical reaction 

Upon reaching the core-mantle boundary, approximately 1,800 miles below the surface, the water triggers a profound chemical reaction. 

This interaction alters the core’s structure, forming a hydrogen-rich, silicon-depleted layer in the topmost outer core, characterized by reduced seismic velocities. This aligns with anomalies previously mapped by seismologists.

High-pressure experiments conducted by the researchers demonstrate that subducted water chemically reacts with core materials, generating silica crystals that rise and integrate into the mantle. This reaction leads to the formation of a modified liquid metallic layer that is less dense and possesses distinct properties.

Study significance 

“For years, it has been believed that material exchange between Earth’s core and mantle is small. Yet, our recent high-pressure experiments reveal a different story. We found that when water reaches the core-mantle boundary, it reacts with silicon in the core, forming silica,” said Shim. 

“This discovery, along with our previous observation of diamonds forming from water reacting with carbon in iron liquid under extreme pressure, points to a far more dynamic core-mantle interaction, suggesting substantial material exchange.”

Extensive global water cycle

This finding not only advances our understanding of Earth’s internal processes but also suggests a more extensive global water cycle than recognized before. 

The altered “film” of the core has profound implications for the geochemical cycles connecting the surface-water cycle with the deep metallic core.

The research marks a significant step forward in geoscience, offering new insights into the complex interactions between Earth’s surface and its deepest layers.

The study was conducted using advanced experimental techniques 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. 

Image Credit: Dan Shim/ASU

The study is published in the journal Nature Geoscience.

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