Encyclopedia
A
continent 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, there are six traditions for naming the continents.
Models
The 7-continent model is taught in
China, parts of
Western Europe, and other
English-speaking countries. The joint-Americas models are most prominent in
Western Europe,
Latin America and Iberia. 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 lists 7 continents and names Oceania.
Historians may use the 5-continent model in which
North Africa is separated from
Sub-Saharan Africa and included in Eurasia or the 4-continent Afro-Eurasian .
They are ranked here according to size.
Interpretations
Geographers and historians often find it useful to define larger landmasses connected by land bridges:
- Africa-Eurasia : 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 , Sahul, and Antarctica. These are single blocks of continental crust 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 . 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 are on or approximate to the South American
continental shelf or slope , they are usually reckoned as parts of North America geopolitically.
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. The
Contiguous or
Coterminous United States means the United States without Alaska or Hawaii , but it is very common for people to say
continental for
contiguous.
- See also List of countries by continent, Satellite images of continents.
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." . As late as 1727 Ephraim Chambers wrote in his
Cyclopędia, "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. The European discovery of 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" 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 . This conception appealed to
Russia, which spans Eurasia, and also appealed 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
metamorphic and
igneous rock 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 from earlier cycles of
subduction, continental collision and break up from plate tectonic activity . 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 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.
See also
