Continent

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A continent (Latin continere, "to hold together") is a large continuous landmass. Image:Continents vide couleurs.png

Image:Dymaxion map unfolded-no-ocean.png

1 Definitions
- 1.1 Models
- 1.2 Interpretations
2 History
3 Geology
4 See also
5 External links

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Definitions

Since geography is defined by local convention, there are several conceptions as to which landmasses qualify as continents, and which might be termed supercontinents (e.g. Africa-Eurasia), microcontinents (e.g. Madagascar or New Zealand), or subcontinents (e.g. South Asia). Seven landmasses and their associated islands are commonly reckoned as continents, but these may be consolidated. For example, North and South America are often considered a single continent, and Asia is often united with Europe. Ignoring cases where Antarctica is omitted, or where Australasia or Oceania are used in place of Australia, there are half a dozen traditions for naming the continents.

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Models

Models
7 continents:	Antarctica	South America	North America	Europe	Asia	Africa	Australia
6 continents:	Antarctica	America		Europe	Asia	Africa	Australia
6 continents:	Antarctica	South America	North America	<center>Eurasia		Africa	Australia
5 continents:	Antarctica	<center>America		<center>Eurasia		Africa	Australia
5 continents:	Antarctica	South America	<center>Laurasia			Africa	Australia
4 continents:	Antarctica	<center>America		<center>Africa-Eurasia			Australia

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. 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, the government-approved Atlas of Canada names 7 continents and indicates Oceania instead.

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.

Size
continent	area (km²)
Africa-Eurasia	85 000 000
Laurasia	79 180 000
Eurasia	54 700 000
Asia	44 310 000
America	42 320 000
Africa	30 300 000
North America	24 480 000
South America	17 840 000
Antarctica	13 720 000
Europe	10 390 000
Australia	8 500 000

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Interpretations

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

Africa-Eurasia (also called Eurafrasia): the combined land mass of Africa and Eurasia;
Laurasia: the combined land mass of Eurasia and North America, which were connected by Beringia during the Ice Age;
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.

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.Image:United Nations geographical subregions.png

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.

When the Continent is referred to without clarification by a speaker of British English, 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. 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.

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History

In its original sense, continent meant (and still means) "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." 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 America in 1492 made four (or two, as Chambers still counted them); 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 perspective, the continent with the least reason for separate recognition is Europe, and in scientific circles people generally prefer to subsume Europe and Asia into Eurasia. This conception appealed to Russia, which spans Eurasia, and in Russia and (at least formerly) in Eastern Europe, Eurasia is or was taught as being one of six continents.

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Geology

The surface of the Earth consists of several tectonic plates which move on a plastic layer of the Earth called the asthenosphere. The plates are composed of both continental and oceanic crust. Continental crust is primarily granitoid rock, overlain by a thin veneer of sedimentary rock. Much of the continental crust extends above sea level as dry land. Geographic continents do not correspond with tectonic plates. For example, Asia and North America share the North American plate in the Bering Sea region, and many times over the past few million years Asia and North America were connected by dry land to form a land mass called Laurasia. Asia contains not only the Eurasian plate, but the Arabian plate, the Australian plate (on which India is colliding with Eurasia), and the North American plate. Depending on which continental model one uses, geographic continents can straddle a variable number of tectonic plates. Occasionally there are calls for the continents to be defined by the tectonic plates that carry them. However, not only would this make Arabia on the Arabian plate and India on the Indian plate continents, but it would separate Central America (on the Caribbean plate) from North America and California west of the San Andreas fault (on the Pacific plate) from North America, so this definition has never been widely accepted.

The tectonic plates shift on geologic timescales, a process known as continental drift. Consequently, in the geological past other continents existed, such as the supercontinent Gondwana. (See Category:Historical continents.)

A continent can also be defined as a block of continental crust, which it is in the case of historical continents like Gondwana. In this conception shallow inland seas which flood the margins of these blocks, such as the Bering Sea, are irrelevant; therefore today Africa, Eurasia, and America constitute one geologic supercontinent, Australia-New Guinea comprise a second, and Antarctica a third. However, there are also other, smaller bits of continental crust, called microcontinents, which are too small to be considered continents in the popular geographic conception. These include Madagascar, the Seychelles (the northern Mascarene Plateau), New Zealand, and New Caledonia. Note that volcanic Iceland is an exposed bit of oceanic crust at the mid-ocean ridge, and therefore not a microcontinent.

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