December 2, 2023


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An unknown phenomenon creates a mysterious new layer: ScienceAlert

An unknown phenomenon creates a mysterious new layer: ScienceAlert

Water from Earth’s surface can find its way deep into the planet, and new research explains how it changes the outer region of the liquid metallic core.

The discovery could explain the presence of a thin layer of material inside the planet that has puzzled geologists for decades.

The Earth’s crust is made up of tectonic plates that grind and slide under each other; Over billions of years, this Subduction The areas moved the water down cloak.

When this water reaches the core boundary of the mantle, about 2,900 kilometers (1,800 miles) below the surface, it triggers a powerful chemical reaction. A team from South Korea, the US and Germany showed that this creates a hydrogen-rich upper layer, sending silica into the lower mantle.

“For many years, the physical exchange between the Earth’s core and mantle was thought to be minimal.” He says Materials scientist Dan Shim of Arizona State University.

“However, our recent experiments at high pressure reveal a different story. We found that when water reaches the boundary between the core and mantle, it reacts with silicon in the core, forming silica.”

Illustration of the Earth’s interior revealing subducting water. (Yonsei University)

the Outer coreThe mixture of iron and nickel plays an important role in generating the Earth’s magnetic field, which essentially protects life on the planet from solar wind and radiation. So it’s important to understand how the Earth’s interior works and how it evolved over time.

The boundary between the Earth’s core and mantle changes sharply from silicate to metallic, and little is known about the chemical exchanges.

For decadesRegister researchers Seismic waves Through the Earth’s viscous interior, a thin layer more than a few hundred kilometers thick has been documented, but until now no one has known where this proposed “E Prime” layer came from.

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“We suggest that such chemical exchange between the core and mantle over gigayears of deep water transport may have contributed to the formation of the putative protostratum E.” He writes.

Seismologists have mapped some unusual features that suggest this altered, liquid mineral layer will be less dense and have slower seismic velocities. These density differences are thought to involve different concentrations of light elements, such as hydrogen or silicon.

But an increase in the concentration of a single optical element would cause the velocity to increase while the density to decrease, making it difficult to reconcile seismic observation with the dynamic stability of the primary E layer.

Increasing the concentration of one light element while decreasing the concentration of another has been put forward as a possible explanation. However, scientists were not aware of this exchange process.

The team used a hot laser Diamond anvil cells To mimic the pressure and temperature conditions at the core-mantle boundary.

They showed that water soaked into the Earth’s core could chemically react with materials there to transform the outer core into a hydrogen-rich layer and disperse silica crystals that rise and join the mantle.

Crystal-like structures rising from the fiery liquid
Illustration of silica crystals emerging from the liquid metal in the Earth’s outer core due to subducting water, which causes a chemical reaction. (Dan Shim/Arizona State University)

The layer of hydrogen-rich, silicon-poor material that forms at the top of the core will have a lower density and lower velocity, consistent with observations of seismic waves.

The changing base film, in turn, may have a significant impact on the film Deep water cycleThe team says their findings point to a global water cycle that is more complex than we thought.

“This discovery, along with our Previous note Of diamonds formed by the reaction of water with carbon in liquid iron under extreme pressure.” Shim He says“It indicates a much more dynamic interaction between the core and the mantle, indicating a significant physical exchange.”

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The study was published in Natural earth sciences.