Continent
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A continent (Latin continere, "to hold together") is a large continuous landmass.
Classifications
Since geography is defined by local convention and there is difficulty in setting lines in terms of "continuous", there are several variations as to which land masses qualify as continents, and which must be classified as supercontinents, microcontinents, subcontinents or islands. 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 (when considered as the largest island of the globe), there are half a dozen traditions for naming the continents.
Models
| Models | ||||||||
|---|---|---|---|---|---|---|---|---|
| 8 continents: | Antarctica | South America | North America | Central America | Europe | Asia | Africa | Oceania |
| 7 continents: | Antarctica | South America | Europe | Asia | Africa | Oceania | ||
| 7 continents: | Antarctica | South America | Europe | Asia | Africa | Australia | ||
| 6 continents: | Antarctica | South America | Europe | Asia | Africa | |||
| 6 continents: | Antarctica | Europe | Asia | Africa | Oceania | |||
| 6 continents: | Antarctica | Europe | Asia | Africa | Australia | |||
| 6 continents: | Antarctica | South America | Africa | Oceania | ||||
| 6 continents: | Antarctica | South America | Africa | Australia | ||||
| 5 continents: | Antarctica | Africa | Oceania | |||||
| 5 continents: | Antarctica | Africa | Australia | |||||
| 5 continents: | Antarctica | South America | Africa | |||||
| 5 continents: | Europe | Asia | Africa | Oceania | ||||
| 5 continents: | Antarctica | Africa | Oceania | |||||
| 5 continents: | Antarctica | Africa | Australia | |||||
| 4 continents: | Antarctica | Oceania | ||||||
| 4 continents: | Antarctica | Australia | ||||||
| 4 continents: | Antarctica | Africa | ||||||
| 3 continents: | Antarctica | |||||||
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 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, 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 |
| Americas | 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 |
| Oceania | 8 500 000 |
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.
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.
History
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." 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 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.
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 aged metamorphic and igneous rock (typically 1.5 to 3.8 BY 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) 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, distince ancient shield areas and a distinct newer mobile belt (the Urals) forming the mutual margin. Also, India isa 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 and the connecting istmus 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.
See also
External links
