Thermodynamics of light elements stratification in the earth's outer core and implications

Thermodynamic calculations, accounting for the effects of changing P, T, and gravitational potential, have been performed to determine the radial distribution of the light elements O, S, Si and C in the outer core of the Earth. It is found that under equilibrium conditions the light elements should be stratified within the top 200–400 km of the outer core, increasing rapidly in concentration with radial distance within this range. The high oxygen content of ∼13 wt % at the top of the core inferred from consideration of core-mantle equilibrium matches the calculated O-concentration profile for the bulk O content of ∼ 2 wt %. The evolution of the core toward the state of thermodynamic equilibrium prior to the destabilizing effect of vigorous convection triggered by the inner core formation provides a possible explanation of the stratification of the core near the core-mantle boundary (CMB), as inferred from geophysical data. Similar stratification should also be expected within the core of Mars and other planets with sufficiently large mass of liquid iron, with that in the former being much thicker than in the Earth's core, thereby possibly causing early extinction of its magnetic field. Because of the potential stratification of K into the top part of the core, the role of ⁴⁰K to ⁴⁰Ar decay as an energy source to power the geodynamo becomes problematic.