Carbon is not only essential to life and Earth’s habitability but also traces and modifies geological processes of subduction, partial melting, degassing and change in the composition of rocks, providing valuable insights into Earth’s evolution.
Over the history of the planet, carbon transport between surface and deep reservoirs has impacted the atmospheric, oceanic and crustal CO2 budges together with the composition and state of the Earth’s mantle. Carbon is transported from Earth’s surface to its interior mainly as carbonate minerals in subduction zones and is returned through volcanic degassing.
Current estimates of the carbon distribution in Earth’s mantle are uncertain. This is due partly to limited understanding of the fate of carbonates through subduction, the main process that transports carbon from Earth’s surface to its interior. Oxidized carbon carried by subduction has been found to be present in MgCO3 throughout much of the mantle. Experiments demonstrate that at deep mantle conditions MgCO3 reacts with silicates to form CaCO3. In combination with previous work showing that CaCO3 is more stable than MgCO3 under conditions of Earth’s lowermost mantle, these observations allow us to predict that the signature of surface carbon reaching Earth’s lowermost mantle may include CaCO3.
“We know that the vast majority of Earth’s carbon isn’t up in the atmosphere, it’s in the interior, but our guess as to how much and where depend mostly on measurements of chemical reactions,” said Michigan State University Susannah Dorfman. “Mingda Lv’s work shows that calcium carbonate can be stable in mantle conditions and provides a new mechanism to take into account when we make models of the carbon cycle inside Earth.”