Plate tectonics is primarily caused by Earth's cooling mechanism, which generates convection currents in the planet's mantle that trigger slow but constant tectonic plate movement. This phenomena occurs on the boundaries of adjacent plates, which are classified as divergent, convergent and transform boundaries.
The Earth's outermost mechanical layer is referred to as the lithosphere. This rigid stratum comprises the planet's crust and topmost portion of the mantle. The lithosphere is broken into massive, constantly shifting blocks called plates. The two types of plates are called continental plates and oceanic plates.
Two of the sources of Earth's internal heat are the primordial thermal energy it retained during the planet's initial formation and the decay of radioisotopes. Extreme temperatures within Earth's core generate convection cells that cause the mantle to move. A convection current is produced when warm material moves up, cools and then moves down. As it sinks, the material is re-heated and it moves up again, causing the entire process to repeat. The constant movement of the mantle triggers the plates that are located on top of it to constantly move as well.
Two forces that are influenced by and also initiate mantle convection are known as "ridge push" and "slab pull," or "subduction pull." New crustal plates are formed due to a ridge push, while old plates sink down due to a slab pull. A combination of a ridge push and a slab pull causes oceanic plates to move.