Tectonic plates are composed of the oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust. Faults tend to be geologically active, experiencing earthquakes, volcanic activity, mountain-building, and oceanic trench formation. The relative movement of the plates typically ranges from zero to 10 cm annually. Where the plates meet, their relative motion determines the type of plate boundary (or fault): convergent, divergent, or transform. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s.Įarth's lithosphere, the rigid outer shell of the planet including the crust and upper mantle, is fractured into seven or eight major plates (depending on how they are defined) and many minor plates or 'platelets'. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics (from the Late Latin: tectonicus, from the Ancient Greek: τεκτονικός, lit.'pertaining to building') is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates which have been slowly moving since about 3.4 billion years ago.
