Redox reactions between FeCO3 and H2O in the deep mantle: Significance for the Earth's carbon-hydrogen-oxygen cycles

We propose that the water in deep Earth can provide an abundant source of H2 and O2, which may drive the self-redox reaction of FeCO3 to form appreciable hydrocarbons and O2-bearing phases in the mantle. The former may become the basic nutrient for the evolution of life when these hydrocarbons migrate to the shallow crust, and the latter will fix O2 in the deep Earth and contribute to the redox-inhomogeneous mantle. Our study aims to address a longstanding knowledge gap regarding the redox mechanism(s) in the Fe-C-H-O system up to 90 GPa, 2500 K. The results from this study are expected to quantify structures of CO4-bearing carbonates in the deep lower mantle and the nature of coupled Fe-C-H-O redox reactions. This is of major interest to the broader Earth Science community, including those studying the physicochemical properties of CO4 tetrahedra in carbonates, the genesis of deep hydrocarbons, and the cycling of volatiles and their impact on Earth’s climate and atmosphere.