 Evidence from seismology, heat flow at the surface, and mineral physics is combined with the Earth's mass and moment of inertia to infer models of the Earth's interior – its composition, density, temperature, pressure.For example, the Earth's mean specific gravity () is far higher than the typical specific gravity of rocks at the surface (), implying that the deeper material is denser.This is also implied by its low moment of inertia (, compared to for a sphere of constant density).