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In geology, a continent is defined by continental crust, which is a platform of metamorphic and igneous rocks, largely of granitic composition. Continental crust is less dense and much thicker than oceanic crust, which causes it to "float" higher than oceanic crust on the dense underlying mantle. This explains why the continents form high ...
In geography, different geographic (scale) levels are distinguished: The local scale level relates to a small area, usually a city or municipality; The regional scale level relates to a larger area, usually a region, state or province; The national scale level relates to a country; The continental scale level refers to a continent;
The thickness of Earth's crust (km). The continental crust consists of various layers, with a bulk composition that is intermediate (SiO 2 wt% = 60.6). [5] The average density of the continental crust is about, 2.83 g/cm 3 (0.102 lb/cu in), [6] less dense than the ultramafic material that makes up the mantle, which has a density of around 3.3 g/cm 3 (0.12 lb/cu in).
Map showing Earth's principal tectonic plates and their boundaries in detail. These plates comprise the bulk of the continents and the Pacific Ocean.For purposes of this list, a major plate is any plate with an area greater than 20 million km 2 (7.7 million sq mi)
(Definitions of "continents" are a physical and cultural construct dating back centuries, long before the advent or even knowledge of plate tectonics; thus, defining a "continent" falls into the realm of physical and cultural geography (i.e. geopolitics), while continental plate definitions fall under plate tectonics in the realm of geology.)
Major continental divides, showing drainage into the major oceans and seas of the world. Grey areas are endorheic basins that do not drain to the ocean.. A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...
The continental shelf is the relatively shallow water area found in proximity to continents; it is the portion of the continental margin that transitions from the shore out towards to ocean. Continental shelves are believed to make up 7% of the sea floor. [3] The width of continental shelves worldwide varies in the range of 0.03–1500 km. [4]
Continental landmasses are not usually classified as islands despite being completely surrounded by water. [ Note 1 ] However, because the definition of continent varies between geographers, the Americas are sometimes defined as two separate continents while mainland Australia is sometimes defined as an island as well as a continent.