The Earth’s core is the largest carbon store on Earth: about 90% of it is buried there. Scientists have discovered the processes by which they can be created. large amount of diamonds at the core-mantle boundaryseveral thousand kilometers deep.
Scientists have shown that hydrated minerals, that is, water-containing minerals, can descend from the oceanic crust to the Earth’s interior, specifically the boundary between the core and the mantle, through the subduction process.
The temperature at the core-mantle boundary is at least twice the temperature of the lava.and high enough so that water can be expelled from the hydrated minerals. Therefore, a chemical reaction similar to the oxidation of steel can occur at the boundary between the Earth’s core and the mantle.
Collaborators with Byeongkwan Ko of Arizona State University have published their findings on the mantle-core boundary. Geophysical Research Letters. This group of scientists conducted experiments at the Advanced Photon Source at Argonne National Laboratory in which they compressed an alloy of iron, carbon, and water to pressure and temperature at the boundary between Earth’s core and mantle. , so they melted an alloy of iron and carbon. .
diamond is formed
The researchers found that water and metal react to produce iron oxides and hydroxides, just as rust forms on the Earth’s surface. However, due to conditions at the core-mantle boundary, carbon comes out of the liquid iron-metal alloy and forms diamond.
“At 3,000 km deep, the temperature at the boundary between the silicate mantle and the metallic core reaches about 3,800ºC, which is high enough for most minerals to lose the H2O trapped in their atomic-scale structures. Professor at the ASU School of Science.”In fact, the temperature is high enough for some minerals to melt under these conditions.”Add.
Since carbon is an iron-loving element, a significant amount of carbon is expected to be present in the core, while relatively little carbon is thought to be present in the mantle. But scientists have discovered that there is much more carbon in the mantle than expected.
“At the pressure at the Earth’s core-mantle boundary, alloying hydrogen with liquid iron metal seems to reduce the solubility of other light elements in the core,” Shim said. Said. “Therefore, the solubility of carbon, presumably in the Earth’s core, decreases locally (through dehydration) where hydrogen enters the core from the mantle. The stable form of carbon under conditions of pressure and temperature at the boundary between the Earth’s core and the mantle is diamond.. So the carbon that escaped from the liquid outer core would turn into diamond when it entered the mantle.”
“Carbon is an essential element for life and plays an important role in many geological processes,” Ko recalled. “The new discovery of a mechanism of carbon transfer from the core to the mantle will shed light on understanding the carbon cycle in the deep. Earth’s interior, which is even more exciting, because Diamond formation at the core-mantle boundary could have been going on for billions of years since the beginning of subduction on the planet”.
Ko’s new work shows that leaching of carbon from the core to the mantle by this diamond-forming process could provide enough carbon to explain the high amount of carbon in the mantle. Ko and collaborators suggest that diamond-rich structures may exist at the core-mantle boundary, and in addition, seismic surveys can detect such structures because seismic waves must travel unusually fast for structures.
“The reason why seismic waves propagate extraordinarily fast along diamond-rich structures at the core-mantle boundary is that diamond is extremely incompressible and less dense than other materials at the core-mantle boundary. Cape,” explained Shim.
Ko and his team will continue to explore how the reaction could change the concentration of other light elements such as silicon, sulfur and oxygen in the core and how these changes might affect deep mantle mineralogy.
Reference Work: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL098271
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