Diamonds and rust border the Earth’s mantle

Diamonds and rust border the Earth's mantle

The iron-carbon alloy reacted with water at the high pressure and high temperature conditions related to the deep Earth mantle in the diamond anvil cell. Credit: Arizona State University

Steel rusts with water and air on the surface of the earth. But what about the depths of the earth’s interior?

Earth’s core is the largest carbon Storage on the floor – almost 90% are buried there. Scientists have shown that oceanic crust which sits on top of tectonic plates and falls inland, through subduction, contains hydrated minerals and can sometimes descend all the way to the core-cloak the border. The temperature at the core-mantle boundary is at least twice that of lava, high enough that water can be released from the hydrated minerals. Therefore, a chemical reaction similar to steel rusting can occur at the boundaries of the Earth’s mantle.

Byungkwan Koo, recently received a Ph.D. from Arizona State University. He and his collaborators produce their findings about the primary mantle boundary in Geophysical Research Letters. They conducted experiments at the Advanced Photon Source at Argonne National Laboratory, compressing iron-carbon alloys and water together to the expected pressure and temperature at Earth’s core boundary, melting the iron-carbon alloy.

Researchers have found that water and metal react and make iron oxides and iron hydroxides, just as it does with rust on the Earth’s surface. However, they found that for core-mantle boundary conditions, carbon exits from iron-metal alloys and forms diamonds.

“The temperature at the boundary between the silicate mantle and the mineral core at a depth of 3,000 km reaches nearly 7,000 F, which is high enough that most minerals H2“O has been captured in their atomic structures. In fact, the temperature is high enough that some metals melt under such conditions,” said Dan Shim, a professor in Arizona State University’s School of Earth and Space Exploration.

Since carbon is an iron-loving element, a large amount of carbon is expected in the core, while the mantle is believed to have a relatively low carbon content. However, scientists have found that there is much more carbon in the mantle than expected.

“Under the expected pressures of the Earth’s core boundary, mixtures of hydrogen with a liquid metallic iron appear to reduce the solubility of other light elements in the core,” Shim said. “Therefore, the solubility of carbon, potentially in Earth’s core, decreases locally as hydrogen enters the core from the mantle (through dehydration). The constant form of carbon at the pressure and temperature conditions of Earth’s core boundary is diamond. So the carbon escaping from the outer core is diamond. The liquid becomes diamond when it enters the mantle.”

“Carbon is an essential element for life and plays an important role in many geological processesKoo said. “The new discovery of the mechanism of carbon transfer from the core to the mantle will shed light on understanding the carbon cycle in the deep Earth. This is all the more exciting given that diamond formation at the core-mantle boundary may have been ongoing for billions of years since subduction began on the planet.”

Kue’s new study shows that carbon seeping from the core into the mantle through this diamond-forming process may provide enough carbon to explain the high amounts of carbon in the mantle. Koe and his collaborators also speculated that diamond-rich structures could exist within the core mantle and this seismic studies You may detect structures because seismic waves must travel at an unusual speed for the structures.

“The reason seismic waves must propagate at exceptional speed through diamond-rich structures at the core-mantle boundary is that diamond is extremely incompressible and less dense than other materials in the basic mantle borderShim said.

Ko and his team will continue to investigate how the reaction can also change the concentration of other light elements in the core, such as silicon, sulfur and oxygen, and how these changes might affect the mineralogy of the deep mantle.


Isotopes of heavy iron leaking from the Earth’s core


more information:
Byeongkwan Ko et al, Water-induced diamond formation at the Earth’s boundary-mantle mantle, Geophysical Research Letters (2022). doi: 10.1029/2022GL098271

Introduction of
Arizona State University


the quote: Diamond and Rust at Earth’s Core Boundary (2022, August 31) Retrieved August 31, 2022 from https://phys.org/news/2022-08-diamonds-rust-earth-core-mantle-boundary.html

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