“The temperature at the boundary between the silicate mantle and metallic core at 3,000 km depth reaches approximately 7,000 F, which is high enough for most minerals to lose the water captured in their atomic-scale structures,” Dan Shim, one of the scientists involved. in the study, he said in a media release. “In fact, the temperature is high enough for some minerals to melt under these conditions.”
Shim explained that since carbon is an iron-loving element, there is expected to be significant carbon in the core, while the mantle is thought to be relatively low in carbon. However, scientists have discovered that there is much more carbon in the mantle than expected.
“At the pressures expected for the Earth’s core-mantle boundary, hydrogen alloying with liquid metallic iron appears to reduce the solubility of other light elements in the core,” the researcher said. “Therefore, the solubility of carbon, which probably exists in the earth’s core, decreases locally where hydrogen enters the core from the mantle (through dehydration). The stable form of carbon at pressure-temperature conditions of Earth’s core-mantle boundary is diamond. Thus, carbon escaping from the liquid outer core would become diamond as it enters the mantle.”
According to Byeongkwan Ko, who led the Geophysical Research Letters paper presenting these findings, the new discovery of a carbon transfer mechanism from the core to the mantle helps shed light on understanding the carbon cycle in the deep interior of the earth
“This is even more exciting considering that diamond formation at the core-mantle boundary could have been going on for billions of years since subduction began on the planet,” he said.
Ko’s study shows that the leakage of carbon from the core to the mantle through this diamond-forming process can provide enough carbon to explain the high amounts of carbon in the mantle.
He and his collaborators also predicted that diamond-rich structures may exist at the core-mantle boundary and that seismic surveys could detect them because seismic waves should travel unusually fast through the structures.
“The reason why seismic waves must propagate exceptionally fast through diamond-rich structures at the core-mantle boundary is because diamond is extremely incompressible and less dense than other materials at the core-mantle boundary,” he said. said Shim.
Ko, Shim and the rest of the team now plan to continue investigating 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 can affect the mineralogy of the deep mantle. .