Tectonic plates refer to a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. It is also known as the lithosphere plate. The tectonic plates play a major role in making up the foundation of the earth's crust and the shape of the continents. The size of the plate varies from a few hundred to thousands of kilometers across; the Pacific and Antarctic Plates are among the largest. The thickness of the tectonic plates also ranges from less than 15 km for young oceanic lithosphere to about 200 km or more for ancient continental lithosphere.
The tectonic plates comprises of two types of lithosphere. They are the thicker continental and thin oceanic. The upper part of the plates is known as the crust. The tectonic plate can be of one type, or of both types. The theory keenly proposes the amount of surface of the plates that disappear in the mantle along the convergent boundaries by subduction is more or less in equilibrium with the new (oceanic) crust that is formed along the divergent margins by seafloor spreading. This is referred to as the "conveyor belt" principle. Therefore the total surface of the globe remains the same.
The tectonic plates causes the underneath mantle to constantly reticulate which causes in floatation of the plates around slowly in a process called tectonic drift. The theory of plate tectonics describes this in a way which solved several scientific dilemmas about the distribution of species when it was introduced. The process when the plates push up against each other, they create mountain ranges and volcanoes. For example Mt. Everest was created in this way. The plates are so large that each wraps makes them curved over a considerable portion of the earth's surface.