Hydrogen in the Earth's core

Abstract

The density of the Earth's core is 8–10% less than that of pure iron at the same pressure and temperature and this is usually interpreted as implying the existence of a substantial amount of light element(s) in the core. Many possibilities have been considered, with sulphur and oxygen receiving most recent attention, but in this note the discussion is limited to hydrogen's contribution to the density deficit. It is shown that hydrogen is not only effective in decreasing the density but is also highly soluble in iron in the relevant conditions. Only about 1% by mass of hydrogen is required in the Earth's core to explain the density deficit, and this corresponds to a hydrogen–iron mass ratio that is only about one-tenth of that present in type I carbonaceous chondrites. The significance of hydrogen as a contributor to the density deficit is, therefore, determined by the extent to which the Earth-forming matter consisted of low temperature condensates.