Abstract
Carbon and hydrogen are possible candidates of the light elements in the Earth's core. I report effects of carbon and hydrogen on the melting temperature and density of the Earth's core. To investigate phase relations and thermoelastic properties of iron-carbide and -hydride, high-pressure experiments were performed using Kawai-type apparatus and diamond anvil cell. From phase relation in the Fe-C system, it was found that Fe7C3 rather than Fe3C could be the stable phase under the core pressures and one of the candidates of the inner core constituent. On the basis of equations of state for Fe7C3 and γ-FeHx, carbon and hydrogen can reasonably reduce the density of pure Fe to explain the core density deficit. If carbon and hydrogen are the major light elements in the core, the temperature of the core should be lower than previous estimates.
