The tectonic plates of the world were mapped in the second half of the 20th century.
The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which "float" on the fluid-like asthenosphere.
Tectonic plates are comprised of two types of lithosphere: continental and oceaniclithospheres; for example, the African Plate includes the continent and parts of the floor of the Atlantic and Indian Oceans.