The bowels of the Earth hide many unsolved mysteries, including one being the “diamond factory” which is thought to have existed billions of years ago.
Of note, carbon plays an important role in the geological processes that occur inside the Earth. Most of the carbon on our planet is in its core. However, it is not known for certain whether core carbon can be added to the Earth’s mantle or not due to the lack of knowledge on possible carbon transfer mechanisms at the core-mantle boundary.
In the new study, a team of geoscientists led by Arizona State University and Michigan State University conducted experiments reproducing the extreme pressure and temperature conditions of the core-mantle boundary.
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Their results show that water can react with metallic iron cores and release carbon like diamond. This process demonstrates an important relationship between the water and carbon cycles on Earth. Furthermore, their results predict the possible presence of diamonds in some regions of the deeper mantle.
“Carbon is an essential element for life and plays an important role in many geological processes,” said Dr. Byeongkwan Ko, postdoctoral researcher at Michigan State University, quoted by Sci News.
“The discovery of a new mechanism of carbon transfer from the core to the mantle will shed light on the understanding of the carbon cycle within the Earth. This is even more interesting considering that the formation of diamonds at the core-mantle boundary may be gone. . for billions of years since the onset of subduction on the planet, “he explained.
In their experiment, Dr. Ko and colleagues compressed the iron-carbon alloy and water to the desired pressure and temperature at the boundary between the core and the Earth’s mantle, then melted the iron-carbon alloy.
They found that water and metals react to form iron oxides and iron hydroxides, as happens with rust on the earth’s surface. However, they found that due to the core-mantle boundary conditions, carbon exits the molten iron-metal alloy and forms the diamond.
“The temperature at the boundary between the silicate mantle and the metal core at a depth of 3,000 km reaches around 3,900 degrees Celsius, a temperature high enough to allow most minerals to lose the water captured in their atomic-scale structure.” , said Professor Dan Shim, a researcher at Arizona State University. .
“In fact, the temperature was high enough for some minerals to melt under these conditions,” he added.
Since carbon is an iron-loving element, it is believed that significant carbon is present in the core, while the mantle is thought to have relatively low carbon. However, geoscientists have found that there is more carbon in the mantle than previously thought.
‘At the predicted pressure at the Earth’s core-mantle boundary, alloying hydrogen with molten ferrous metal appears to reduce the solubility of other light elements in the core,’ said Professor Shim.
Therefore, the solubility of carbon, which is likely present in the Earth’s core, decreases locally where the hydrogen enters the core from the mantle (through dehydration).
Well, the stable form of carbon under the temperature-pressure boundary conditions of the Earth’s core-mantle is diamond. ‘So the carbon that comes out of the molten outer core becomes diamond when it enters the mantle,’ said Professor Shim.
The current study suggests that carbon leaking from the core into the mantle from this diamond-forming process could provide enough carbon to explain the increased amount of carbon in the mantle.
The researchers also predict that diamond-rich structures could exist at the core-mantle boundary, and seismic studies could detect these structures because seismic waves must travel very fast for these structures.
‘The reason seismic waves must propagate so rapidly through the diamond-rich structure at the core-mantle boundary is that diamond is highly incompressible and less dense than other materials at the core-mantle boundary,’ concluded Professor Shim. .
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(rns / fyk)