The Composition of the Lower Mantle and Core

This chapter examines the composition of the core and of the mantle and its domains, upper and lower, its physical and chemical attributes, and its evolution. It starts with fundamental definitions, particularly of what is the lower and upper mantle. Although a compositional model for the lower mantle that matches that of the upper mantle for major elements is most compatible with observations and constraints, uncertainties are such that competing compositional models are tenable. Based on chondritic models, more than 90% of the mass for the Earth is composed of Fe, O, Mg and Si and the addition of Ni, Ca, Al and S accounts for more than 98% by mass the composition of the Earth. Constraints on the absolute and relative abundances of volatile elements in the Earth are consistent with only ~2% by mass of sulfur and a negligible role for H, C or N in the core.