EarthRef.org Reference Database (ERR) -- Ringwood 1966

The Earth has retained primordial abundances of elements not readily volatile under high-temperature reducing conditions. In a model based on this hypothesis, the metallic core contains 20 percent of elemental silicon; the upper mantle is concluded to have a 3:1 ratio of peridotite to basalt. Compared with composition of the entire mantle, derived from chondritic abundances, a distinctive differentiation pattern is revealed. Trace elements not entering major mantle minerals have been concentrated into the upper mantle by crystal-liquid fractionation. High siderophile abundances imply a core formed in chemical disequilibrium with the mantle. Multi-stage theories of reduction before Earth accretion are rejected in favor of direct single-stage accretion in the growing Earth. Volatile elements escaped with the dense primitive atmosphere; non-volatile silicates precipitated in a disk which broke up to form the Moon