Carbon and other Light Elements in Earth's Core

In a recent study, researchers used two-phase first-principles molecular dynamics to derive the partition coefficient of C and several other light elements between liquid iron and silicate melt.

Atomic configurationCarbon (C) is one of the candidate light elements proposed to account for the density deficit of Earth’s core. In addition, C significantly affects the distribution of elements between metals and silicates in Earth’s core and mantle. Therefore, calculating the accretionary and core-mantle segregation history of Earth requires accurate knowledge of carbon’s abundance in the core. Previous estimates of carbon in the core differ by a factor of ~20 due to different assumptions and methods, and because the metal-silicate partition coefficient was previously unknown.

In a recent study, Zhang and Yin [1] used two-phase first-principles molecular dynamics to derive the partition coefficient of C and several other light elements between liquid iron and silicate melt. The research team calculated a value of 9 + 3 at 3,200 K and 40 GPa. Using this partition coefficient and the most recent estimates of bulk Earth or mantle C contents, the researchers inferred that Earth’s core contains 0.1 to 0.7 wt% of carbon. This estimate falls in the lower range of the previous estimates—which ranged from 0.2 to 4.0 wt%. The current estimate suggests that carbon plays a moderate role in the density deficit of the core and in the distribution elements having affinities for iron or sulfur during core mantle segregation.
 
Figure:  (Upper) Snapshot of atomic configuration in the simulation cell after the center of mass of the Fe cluster is moved to the center of the simulation cell and all of the atoms are moved accordingly by using the periodic conditions of the simulation cell.  The encircled area marks the liquid metal phase domain and the surrounding area is the silicate melt domain. (Lower) The constructed alpha shape of the Fe cluster showing Fe atoms on the surface of the alpha shape and the Si and C atoms enclosed in the alpha shape. 

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