과학자들은 맨틀에 예상보다 훨씬 많은 탄소가 있다는 것을 발견했습니다.
연구원들은 지구의 핵심층 경계에서 녹과 다이아몬드를 발견했습니다.
지구 표면에서 강철은 물과 공기로 인해 녹슬게 됩니다. 그러나 지구 내부의 깊이는 어떻습니까?
지구상에서 가장 큰 탄소 저장고는 탄소의 90%가 묻혀 있는 지구의 핵심부입니다. 과학자들은 지각판 위에 자리잡고 내륙으로 떨어지는 해양 지각이 수화된 광물을 포함하고 있으며 때때로 코어와 맨틀 사이의 경계에 도달할 수 있음을 보여주었습니다. 코어-맨틀 경계에서 온도는 적어도 용암의 두 배이며 수화된 광물에서 물이 빠져나갈 수 있을 만큼 충분히 높습니다. 그 결과 지구의 맨틀 경계 근처에서 강철의 녹과 유사한 화학 반응이 발생할 수 있습니다.
최근 Ph.D. 에서 나가다 애리조나 주립대학교, 그리고 동료들은 지구물리학 연구 레터(Geophysical Research Letters) 저널에서 코어 맨틀 경계에 대한 연구 결과를 보고합니다. 그들은 고급 광자 소스로 실험을 수행했습니다. 아르곤 국립 연구소압력 및 가열 물과 탄소 철[{” attribute=””>alloy to conditions similar to those at the Earth’s core-mantle boundary, melting the iron-carbon alloy.
The iron-carbon alloy reacted with water at high pressure and high-temperature conditions related to the Earth’s deep mantle in a diamond-anvil cell. Credit: Arizona State University
The scientists discovered that water and metal react to form iron oxides and iron hydroxides, just like rusting on Earth’s surface. However, they observed that at the core-mantle boundary conditions, carbon separates from the liquid iron-metal alloy and forms diamonds.
“Temperature at the boundary between the silicate mantle and the metallic core at 3,000 km depth reaches to roughly 7,000 F, which is sufficiently high for most minerals to lose H2O captured in their atomic-scale structures,” said Dan Shim, professor at ASU’s School of Earth and Space Exploration. “In fact, the temperature is high enough that some minerals should melt at such conditions.”
Because carbon is an iron-loving element, significant carbon is expected to exist in the core, while the mantle is thought to have relatively low carbon. However, scientists have found that much more carbon exists in the mantle than expected.
“At the pressures expected for the Earth’s core-mantle boundary, hydrogen alloying with iron metal liquid appears to reduce the solubility of other light elements in the core,” said Shim. “Therefore, the solubility of carbon, which likely exists in the Earth’s core, decreases locally where hydrogen enters into the core from the mantle (through dehydration). The stable form of carbon at the pressure-temperature conditions of Earth’s core-mantle boundary is diamond. So the carbon escaping from the liquid outer core would become diamond when it enters into the mantle.”
“Carbon is an essential element for life and plays an important role in many geological processes,” said Ko. “The new discovery of a carbon transfer mechanism from the core to the mantle will shed light on the understanding of the carbon cycle in the Earth’s deep interior. This is even more exciting given that the diamond formation at the core-mantle boundary might have been going on for billions of years since the initiation of subduction on the planet.”
Ko’s new study shows that carbon leaking from the core into the mantle by this diamond formation process may supply enough carbon to explain the elevated carbon amounts in the mantle. Ko and his collaborators also predicted that diamond-rich structures can exist at the core-mantle boundary and that seismic studies might detect the structures because seismic waves should travel unusually fast for the structures.
“The reason that seismic waves should propagate exceptionally fast through diamond-rich structures at the core-mantle boundary is that diamonds are extremely incompressible and less dense than other materials at the core-mantle boundary,” said Shim.
Ko and the team will 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 such changes can impact the mineralogy of the deep mantle.
Reference: “Water-Induced Diamond Formation at Earth’s Core-Mantle Boundary” by Byeongkwan Ko, Stella Chariton, Vitali Prakapenka, Bin Chen, Edward J. Garnero, Mingming Li and Sang-Heon Shim, 11 August 2022, Geophysical Research Letters.
DOI: 10.1029/2022GL098271
