Plate tectonics is the theory that states that Earth's outer shell is divided into several plates that glide over the mantle. The plates act like a hard and rigid shell compared to Earth's mantle. This strong outer layer is called the lithosphere. Plate tectonics is the modern version of continental drift. The plates consist of two principal types of material, oceanic crust, and continental crust. The earth is considered to have 15 major tectonic plates. Seven of which are primary plates and the rest are secondary plates. The primary plates are the African plate, the Antarctic plate, the Eurasian plate, the Indo-Australian plate, the North American plate, the Pacific plate, and the South American plate. The secondary plates are the Arabian plate, the Caribbean plate, the Cocos plate, the Juan de Fuca plate, the Indian plate, the Nazca plate, the Philippine Sea plate and the Scotia plate