Observational constraints on the thermal and compositional structure of the earth

This chapter summarizes diverse observations pertaining to heat flow inside the Earth. Information on temperatures, flux, various material properties, heat sources, internal layering, and lateral differences are summarized because they pertain to the boundary and initial conditions used to construct thermal models of planets. We show how the presence and location of molten layers constrain both temperatures and flux, and discuss the implications for Earth’s thermal structure and evolution. Problems in assuming adiabatic gradients and internal homogeneity are discussed. Energy sources in addition to radionuclide decay are covered: we show that an important gravitational source, dissipation of spin via friction during differential rotation, has been overlooked. Spin exerts crucial control on plate tectonics, as proved by abundant evidence reviewed here.