Continent

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A continent (Latin continere, "to hold together") is a large continuous landmass.

A world map depicting the traditional geographic continents. Land boundaries between nation-states are also shown.

Dymaxion map by Buckminster Fuller shows land masses with minimal distortion as nearly one continuous continent

[edit] Classifications

Since geography is somewhat defined by local convention and there may be difficulty in delineating the continuity of a landmass, there are several variations as to which landmasses are considered continents and which are not. Seven landmasses and their associated islands are commonly reckoned as continents (in order of decreasing area) – Asia, Africa, North America, South America, Antarctica, Europe, and Australia – but some of these may be consolidated. For example, North and South America are often considered a single continent (America), as are Europe and Asia (Eurasia). Ignoring cases where Antarctica is omitted, or where Australasia or Oceania are used in place of Australia, there are at least seven major traditions for naming the continents.

[edit] Models

The 7-continent model is usually taught in Western Europe, China, and most native English-speaking countries. The 6-continent combined-America model is taught in Latin America, Iberia, Italy and some other parts of Europe. The 6-continent combined-Eurasia model is preferred by the geographic community, Russia, Eastern Europe, and Japan. In all of these cases, the names Australasia or Oceania may be used in place of Australia. In Canada, for example, the government-approved Atlas of Canada lists 7 continents and names Oceania.^[1]

Historians may use the 5-continent model in which North Africa is separated from Sub-Saharan Africa and included in Eurasia (Jared Diamond) or the 4-continent Afro-Eurasian (Andre Gunder Frank).

They are ranked here according to size and population.

[edit] Interpretations

Geographers and historians often find it useful to define larger landmasses connected by land bridges:

1. Africa-Eurasia (also called Eurafrasia): the combined land mass of Africa and Eurasia;
2. Laurasia: the combined land mass of Eurasia and North America, which were connected by Beringia during the Ice Age;
3. Sahul: the combined land mass of Australia, New Guinea, and Tasmania during the Ice Age.

That is, during the last Ice Age, there were three large landmasses: Africa-Eurasia + America (which has no name), Sahul, and Antarctica. These are single blocks of continental crust (see below) and therefore continents or supercontinents in the geological sense even today.

A world map of continental regions and their subregions in use by the United Nations

Continents are sometimes subdivided into subcontinents that are delineated by geological features: the prototype of this is the Indian subcontinent. In the last century, it has also become customary to subdivide major landmasses, particularly Eurasia and the Americas, into regions or subregions of varying size and scope; for instance, the Indian subcontinent somewhat corresponds to South Asia.

Islands are usually considered to belong geographically to the continent they are closest to. The Coral Sea and South Pacific islands may be associated with Australia/Australasia to form the "continent" of Oceania (though the Pacific islands without Australia are also called Oceania). The British Isles have always been considered part of Europe, and Greenland is considered part of North America. Conversely, while a number of the islands of the Caribbean (West Indies) are on or approximate to the South American continental shelf or slope (e.g., Aruba, Netherlands Antilles, Trinidad and Tobago), they are usually reckoned as parts of North America geopolitically. [1] [2] [3]

When the Continent is referred to without clarification by a speaker of British English from Europe, it is usually presumed to mean Continental Europe, that is, Europe excluding the British Isles. Elsewhere, islanders may refer to the nearest mainland as simply the Continent. The Continental United States excludes Hawaii. The Contiguous or Co(n)terminous United States means the United States without Alaska or Hawaii (the "Lower 48"), but it is very common for people to say continental for contiguous.

See also List of countries by continent, Satellite images of continents.

[edit] History of the concept

In its original sense, continent meant "mainland". In the Greco-Roman world, this Continent was the entire known world; it was divided into three parts: Europe, Asia, and Africa. These were at first called peninsulas but later also came to be called continents, since they were great land masses themselves.

In the mid 1600s Peter Heylin wrote in his Cosmographie that "A Continent is a great quantity of Land, not separated by any Sea from the rest of the World, as the whole Continent of Europe, Asia, Africa." (Collectively Africa-Eurasia or Eurafrasia). As late as 1727 Ephraim Chambers wrote in his Cyclopædia, "The world is ordinarily divided into two grand continents: the old and the new." Through the Middle Ages, the common division of the known world made for three continents in the Western conception: Europe, Africa, and Asia. (See T and O map.) The European discovery of the Americas in 1492 made four; and the European discovery of Australia in 1606 would make five, though not for some time: As late as 1813 geographers wrote of Australia as "New Holland, an immense Island, which some geographers dignify with the appellation of another continent". However, dividing America in two was commonplace by this time, and would also produce a fifth continent. The idea of the Five Continents is still strong in Europe and Asia, and is represented by the five rings on the Olympic flag.

Antarctica was sighted in 1820, for the sixth and last continent to be given a separate name, though a great "antarctic" (antipodean) landmass had been anticipated for millennia. Dividing the Americas in two now made seven continents, nicely symmetrical with the magical number of the Seven Seas, Seven Heavens, and the seven celestial bodies that gave their names to the seven days of the week. However, this division never appealed to Latin America, which saw itself spanning an America that was a single landmass, and there the conception of six continents remains, as it does in scattered other countries such as Japan. From a modern geographic perspective, it could be argued that Europe ought not to be its own continent (in scientific circles people generally prefer to subsume Europe and Asia into Eurasia). This conception appealed to Russia, which spans Eurasia, and also appealed (at least formerly) to Eastern Europe. However, Eurasia is based on one definition of continent, and there is no universal consent as to the definition of that word.

[edit] Geology

Geologists use the term continent in a different manner than geographers. Rather than simply identifying large land masses, geologists have distinct criteria for identifying continents. Continents are portions of the Earth's crust characterized by a stable platform of Precambrian metamorphic and igneous rock (typically 1.5 to 3.8 billion years old) largely of granitic composition, called the craton, and a central "shield" where the craton is exposed at the surface. The craton itself is an accretionary complex of ancient mobile belts (mountain belts) from earlier cycles of subduction, continental collision and break up from plate tectonic activity (see Plate tectonics). An outward-thickening veneer of younger, minimally deformed sedimentary rock covers much of the rest of the craton. The margins of the continents are characterized by currently-active or relatively recently active mobile belts and/or deep troughs of accumulated marine or deltaic sediments. Beyond the margin, there is a: 1) continental shelf and drop off to the basaltic-rock ocean basin; or, 2) the margin of another continent, depending on the current plate-tectonic setting of the continent. A continental boundary does not have to be a body of water. Over geologic time, continents are periodically submerged under large epicontinental seas, and continental collisions result in a continent becoming attached to another continent. The current geologic era is relatively anomalous in that so much of the continental areas are "high and dry" compared to much of geologic history.

It is believed that continents are accretionary crustal "rafts" which, unlike the denser basaltic crust of the ocean basins, are not subjected to destruction through the plate tectonic process of subduction. This accounts for the great age of the rocks comprising the continental cratons.

By the geologists' definition, Europe and Asia are separate continents since they have separate, distinct ancient shield areas and a distinct newer mobile belt (the Ural Mountains) forming the mutual margin. Also, India is a geological continent, as it contains a central shield, and the geologically recent Himalaya mobile belt forms its northern margin. North America and South America are separate continents, the connecting isthmus being largely the result of volcanism from relatively recent subduction tectonics. But the North American continent also includes Greenland, which is a portion of Canadian Shield, and the mobile belt forming its western margin includes the easternmost portion of the Asian land mass.

[edit] See also

• Continental shelf
• Earth science
• Geography
• Geology
• Plate tectonics
• Landform
• Subregion

[edit] References and notes

Continents of the world

Africa-Eurasia

America

Eurasia

Africa

Antarctica

Asia

Australia

Europe

N. America

S. America

Geological supercontinents Gondwana • Laurasia • Pangaea • Pannotia • Rodinia • Columbia • Kenorland • Ur • Vaalbara

Mythical and theorised continents Atlantis • Lemuria • Mu • Terra Australis

Regions of the world

	Africa	Central • Eastern • Northern • Southern • Western
	Americas	Caribbean • Central • Latin • North • Northern • South
	Asia	Central • Eastern • Northern • Southern • Southeastern • Western
	Europe	Central • Eastern • Northern • Southern • Western
	Oceania	Australasia • Melanesia • Micronesia • Polynesia
	Polar	Arctic • Antarctic
	Oceans	Pacific • Atlantic • Indian  • Southern • Arctic