Continent

A continent is a large landmass on a planet or moon. On Earth, seven areas are generally regarded in reference books as continents: North America, South America, Europe, Asia, Africa, Oceania), and Antarctica. The definition can include the landmass and its nearby islands (thus for example, Oceania—formerly called Australasia—consists of more than just Australia). The definition is a conventional one, as continents may share the same landmass: Europe and Asia are separated not by water but by the Ural mountains; together they are sometimes termed Eurasia.

Continents exist for geological reasons. Their crusts are much thicker and lighter than those of oceans, so that they correspond to emerged land. From the point of view of geology, and more precisely in the theory of plate tectonics, there are more continents than in geography. In plate tectonics, for example, Arabia constitutes a separate plate, partially constituted by continental crust.

History

When the concept was first introduced, there were considered to be only two continents, the old and the new, later called the Old and New Worlds. Later, the old continent was subdivided into three continents: Africa, Asia and Europe. Australia was added in the late 19th century to make a total of five. In the 20th century, Antarctica was added and America (the New World) subdivided into two continents.