ESS.2

Although active geologic processes have destroyed or altered most of Earth’s early rock record, evidence from within Earth and from other objects in the solar system are used to infer Earth’s geologic history. Motions of the mantle and its plates occur primarily through thermal convection, which involves the cycling of matter due to the outward flow of energy from Earth’s interior and gravitational movement of denser materials toward the interior. The radioactive decay of unstable isotopes continually generates new energy within Earth’s crust and mantle, providing the primary source of the heat that drives mantle convection. Plate tectonics is the unifying theory that explains the past and current movements of the rocks at Earth’s surface and provides a framework for understanding its geologic history and co-evolution of life.