In a vertical column, the chemical potential of a component is affected by the change of gravitational potential. Thermodynamic calculations of the radial distribution of light elements O, S, Si and C that were suggested to have been dissolved in the outer core (OC) show their content to increase rapidly upwards in the top 300-400 km. These results explain the formation of compositional layering inferred from seismic studies that was earlier thought to be due to the existence of a subadiabatic temperature gradient at the top or diffusion from a compositionally different primitive layer within the OC. Under thermodynamic equilibrium, O content in the OC should be limited to ~1 wt% and of K to ~25 wt%. Powering of the geodynamo through the heat producing decay of 40K to 40Ar does not seem feasible since K should segregate and produce more heat at the top of the OC.