Energy Flows at Earth’s Surface

Two energy flows converge at Earth’s surface: one coming from the Sun and the other from Earth’s interior. Their intensities are very different, the first one being overwhelming. Solar heat is responsible for all processes involving the outer fluid layers of Earth (atmosphere and oceans). In contrast, processes occurring in Earth’s interior, including convection in the core and in the mantle as well as surface manifestations such as seismic and volcanic activity, are unaffected by solar energy, being due only to internal heat. Solar energy only controls the surface temperature of Earth, which is a boundary condition for internal processes. The argument requires use of basic concepts in thermodynamics, such as the radiance and the spectral radiance of a blackbody. The equation of heat conduction in spherical symmetry is derived and solved for a simple model, yielding an approximate temperature profile within Earth.