Bulk Silicate Earth
Primitive mantle composition (Acronyms: BSE)
Bulk Silicate Earth (BSE) refers to the original chemical composition of the silicate part of the Earth after the accretion and separation of a core but prior to differentiation of the first crust. For this reason, BSE is comparable to the composition of the Earth’s “primitive mantle.” There are several models to evaluate the BSE initial composition. The classic model is to infer BSE from the chemical composition of the most primitive, undifferentiated meteorites, i.e., the CI-class carbonaceous chondrites. Using this model, refractory lithophile elements (i.e., those which did not enter the core but remained in the silicate mantle) are given relative abundances as they occur in chondrites. Other models point to differences in ratios of 142Nd/144Nd and 3He/4He between primitive, mantle-derived lavas and chondrites to derive a somewhat different, nonchondritic composition of the primitive mantle.