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A continent is any of several large geographical regions. Continents are generally identified by convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as in the case of Asia or Europe within Eurasia, or a landmass and nearby islands within its continental shelf. Due to these varying definitions, the number of continents varies; up to seven or as few as four geographical regions are commonly regarded as continents. Most English-speaking countries recognize seven regions as continents. In order from largest to smallest in area, these seven regions are Asia, Africa, North America, South America, Antarctica, Europe, and Australia (sometimes called Oceania or Australasia). Different variations with fewer continents merge some of these regions; examples of this are merging Asia and Europe into Eurasia, "Most people recognize seven continents—Asia, Africa, North America, South America, Antarctica, Europe, and Australia, from largest to smallest—although sometimes Asia and Europe are considered a single continent, Eurasia." North America and South America into the Americas (or simply America), and Africa, Asia, and Europe into Afro-Eurasia.
Oceanic islands are occasionally grouped with a nearby continent to divide all the world's land into geographical regions. Under this scheme, most of the island countries and territories in the Pacific Ocean are grouped together with the continent of Australia to form the geographical region of Oceania.
In geology, a continent is defined as "one of Earth's major landmasses, including both dry land and continental shelves". (2025). 9780922152896, American Geological Institute. ISBN 9780922152896 The geological continents correspond to seven large areas of continental crust that are found on the tectonic plates, but exclude small continental fragments such as Madagascar that are generally referred to as microcontinents. Continental crust is only known to exist on Earth.
The idea of continental drift gained recognition in the 20th century. It postulates that the current continents formed from the breaking up of a supercontinent (Pangaea) that formed hundreds of millions of years ago.
While continent was used on the one hand for relatively small areas of continuous land, on the other hand geographers again raised Herodotus's query about why a single large landmass should be divided into separate continents. In the mid-17th century, 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." In 1727, Ephraim Chambers wrote in his Cyclopædia, "The world is ordinarily divided into two grand continents: the Old World and the New World." And in his 1752 atlas, Emanuel Bowen defined a continent as "a large space of dry land comprehending many countries all joined together, without any separation by water. Thus Europe, Asia, and Africa is one great continent, as America is another."Bowen, Emanuel. (1752). A Complete Atlas, or Distinct View of the Known World. London, p. 3. However, the old idea of Europe, Asia and Africa as "parts" of the world ultimately persisted with these being regarded as separate continents.
Earth's major landmasses all have coasts on a single, continuous World Ocean, which is divided into several principal oceanic components by the continents and various geographic criteria." Distribution of land and water on the planet ." UN Atlas of the Oceans (2004). Retrieved 20 February 2007.
The geological definition of a continent has four criteria: high elevation relative to the ocean floor; a wide range of igneous, metamorphic and sedimentary rocks rich in silica; a crust thicker than the surrounding oceanic crust; and well-defined limits around a large enough area.
From the perspective of geology or physical geography, continent may be extended beyond the confines of continuous dry land to include the shallow, submerged adjacent area (the continental shelf)"continent 2, 6" (1996) Webster's Third New International Dictionary, Unabridged. ProQuest. "a large segment of the earth's outer shell including a terrestrial continent and the adjacent continental shelf" and the islands on the shelf (continental islands), as they are structurally part of the continent.
From this perspective, the edge of the continental shelf is the true edge of the continent, as shorelines vary with changes in sea level.Cliff Ollier (1996). Planet Earth. In Ian Douglas (Ed.), Companion Encyclopedia of Geography: The Environment and Humankind. London: Routledge, p. 30. "Ocean waters extend onto continental rocks at continental shelves, and the true edges of the continents are the steeper continental slopes. The actual shorelines are rather accidental, depending on the height of sea level on the sloping shelves." In this sense the islands of Great Britain and Ireland are part of Europe, while Australia and the island of New Guinea together form a continent. Taken to its limit, this view could support the view that there are only three continents: Antarctica, Australia-New Guinea, and a single mega-continent which joins Afro-Eurasia and America via the contiguous continental shelf in and around the Bering Sea. The vast size of the latter compared to the first two might even lead some to say it is the only continent, the others being more comparable to Greenland or New Zealand.
As a cultural construct, the concept of a continent may go beyond the continental shelf to include oceanic islands and continental fragments. In this way, Iceland is considered a part of Europe, and Madagascar a part of Africa. Extrapolating the concept to its extreme, some geographers group the Australian continental landmass with other islands in the Pacific Ocean into Oceania, which is usually considered a region rather than a continent. This divides the entire land surface of Earth into continents, regions, or quasi-continents.
North America and South America are treated as separate continents in the seven-continent model. However, they may also be viewed as a single continent known as Americas. This viewpoint was common in the United States until World War II, and remains prevalent in some Asian six-continent models. The single American continent model remains a common view in European countries like France, Greece, Hungary, Italy, Malta, Portugal, Spain, Latin American countries and some Asian countries.
The criterion of a discrete landmass is completely disregarded if the continuous landmass of Eurasia is classified as two separate continents (Asia and Europe). Physiographically, Europe and the Indian subcontinent are large peninsulas of the Eurasian landmass. However, Europe is considered a continent with its comparatively large land area of , while the Indian subcontinent, with less than half that area, is considered a subcontinent. The alternative view—in geology and geography—that Eurasia is a single continent results in a six-continent view of the world. Some view the separation of Eurasia into Asia and Europe as a residue of Eurocentrism: "In physical, cultural and historical diversity, China and India are comparable to the entire European landmass, not to a single European country. ...." However, for historical and cultural reasons, the view of Europe as a separate continent continues in almost all categorizations.
If continents are defined strictly as discrete landmasses, embracing all the contiguous land of a body, then Africa, Asia, and Europe form a single continent which may be referred to as Afro-Eurasia. Combined with the consolidation of the Americas, this would produce a four-continent model consisting of Afro-Eurasia, America, Antarctica, and Australia.
When sea levels were lower during the Pleistocene , greater areas of the continental shelf were exposed as dry land, forming between Tasmania and the Australian mainland. At those times, Australia and New Guinea were a single, continuous continent known as Sahul. Likewise, Afro-Eurasia and the Americas were joined by the Beringia. Other islands, such as Great Britain, were joined to the mainlands of their continents. At that time, there were just three discrete landmasses in the world: Africa-Eurasia-Americas, Antarctica, and Australia-New Guinea (Sahul).
| Africa | Asia | Europe | America | Antarctica | Australia | UNSD continental regions | ||
In the English-speaking countries, geographers often use the term Oceania to denote a geographical region which includes most of the island countries and territories in the Pacific Ocean, as well as the continent of Australia.
| + Land areas and population estimates | |||
| Earth | 100.0 | ||
| Asia | 29.8 | ||
| Africa | 20.3 | ||
| North America | 16.2 | ||
| South America | 11.9 | ||
| Antarctica | 9.5 | ||
| Europe | 6.7 | ||
| Oceania | 5.7 |
In many of these cases, the "subcontinents" concerned are on different plate tectonics from the rest of the continent, providing a geological justification for the terminology.
Greenland, generally considered the world's largest island on the northeastern periphery of the North American Plate, is sometimes referred to as a subcontinent. This is a significant departure from the more conventional view of a subcontinent as comprising a very large peninsula on the fringe of a continent.
Where the Americas are viewed as a single continent (America), it is divided into two subcontinents (North America and South America) or three (Central America being the third).In Ibero-America, North America usually designates a region (subcontinente in Spanish) of the Americas containing Canada, the United States, and Mexico, and often Greenland, Saint Pierre and Miquelon, and Bermuda; the land bridge of Central America is generally considered a subregion of North America. Norteamérica (Mexican version) / (Spaniard version) . Encarta Online Encyclopedia. 2009. When Eurasia is regarded as a single continent, Asia and Europe are treated as subcontinents.
With the addition of Zealandia in 2017, Earth currently has seven recognized geological continents:
Due to a seeming lack of Precambrian rocks, Zealandia's status as a geological continent has been disputed by some geologists. However, a study conducted in 2021 found that part of the submerged continent is indeed Precambrian, twice as old as geologists had previously thought, which is further evidence that supports the idea of Zealandia being a geological continent.
All seven geological continents are spatially isolated by geologic features.
Ancient Greek thinkers subsequently debated whether Africa (then called Libya) should be considered part of Asia or a third part of the world. Division into three parts eventually came to predominate. From the Greek viewpoint, the Aegean Sea was the center of the world; Asia lay to the east, Europe to the north and west, and Africa to the south. The boundaries between the continents were not fixed. Early on, the Europe–Asia boundary was taken to run from the Black Sea along the Rioni River (known then as the Phasis) in Georgia. Later it was viewed as running from the Black Sea through Kerch Strait, the Sea of Azov and along the Don River (known then as the Tanais) in Russia. The boundary between Asia and Africa was generally taken to be the Nile River. HerodotusHerodotus. Translated by George Rawlinson (2000). The Histories of Herodotus of Halicarnassus. [16] Ames, Iowa: Omphaloskepsis, book 2, p. 18. in the 5th century BCE objected to the whole of Egypt being split between Asia and Africa ("Libya") and took the boundary to lie along the western border of Egypt, regarding Egypt as part of Asia. He also questioned the division into three of what is really a single landmass,Herodotus. Translated by George Rawlinson (2000). The Histories of Herodotus of Halicarnassus . Ames, Iowa: Omphaloskepsis, book 4, p. 38. "I cannot conceive why three names ... should ever have been given to a tract which is in reality one," a debate that continues nearly two and a half millennia later. Herodotus believed Europe to be larger (at least in width) than the other two continents:
I wonder, then, at those who have mapped out and divided the world into Libya, Asia, and Europe; for the difference between them is great, seeing that in length Europe stretches along both the others together, and it appears to me to be wider beyond all comparison.
Eratosthenes, in the 3rd century BCE, noted that some geographers divided the continents by rivers (the Nile and the Don), thus considering them "islands". Others divided the continents by , calling the continents "peninsulas". These latter geographers set the border between Europe and Asia at the isthmus between the Black Sea and the Caspian Sea, and the border between Asia and Africa at the isthmus between the Red Sea and the mouth of Lake Bardawil on the Mediterranean Sea.Strabo. Translated by Horace Leonard Jones (1917). Geographica.[17] Harvard University Press, book 1, ch. 4.[18]
The Roman author Pliny the Elder, writing in the 1st century CE, stated that "The whole globe is divided into three parts, Europe, Asia, and Africa", adding:
I shall first then speak of Europe, the foster-mother of that people which has conquered all other nations, and itself by far the most beauteous portion of the earth. Indeed, many persons have, not without reason, considered it, not as a third part only of the earth, but as equal to all the rest, looking upon the whole of our globe as divided into two parts only, by a line drawn from the river Tanais to the Straits of Gades.
Following the fall of the Western Roman Empire, the Western culture, linked to Latin and the Catholic church, began to associate itself with the concept of Europe. Through the Roman period and the Middle Ages, a few writers took the Isthmus of Suez as the boundary between Asia and Africa, but most writers continued to consider it the Nile or the western border of Egypt (Gibbon). In the Middle Ages, the world was usually portrayed on T and O maps, with the T representing the waters dividing the three continents. By the middle of the 18th century, "the fashion of dividing Asia and Africa at the Nile, or at the Great Catabathmus the farther west, had even then scarcely passed away".Goddard, Farley Brewer (1884). "Researches in the Cyrenaica". The American Journal of Philology, 5 (1) p. 38.
In 1501, Amerigo Vespucci and Gonçalo Coelho attempted to sail around what they considered the southern end of the Asian mainland into the Indian Ocean, passing through Fernando de Noronha. After reaching the coast of Brazil, they sailed along the coast of South America much farther south than Asia was known to extend, confirming that this was a land of continental proportions. On return to Europe, an account of the voyage, called Mundus Novus ("New World"), was published under Vespucci's name in 1502 or 1503,Formisano, Luciano (Ed.) (1992). Letters from a New World: Amerigo Vespucci's Discovery of America. New York: Marsilio, pp. xx–xxi. . although it seems that it had additions or alterations by another writer.Zerubavel, Eviatar (2003). Terra Cognita: The Mental Discovery of America. New Brunswick: Transaction Publishers, pp. 77–79. . Regardless of who penned the words, Mundus Novus credited Vespucci with saying, "I have discovered a continent in those southern regions that is inhabited by more numerous people and animals than our Europe, or Asia or Africa",Formisano, Luciano (Ed.) (1992). Letters from a New World: Amerigo Vespucci's Discovery of America. New York: Marsilio, p. 45. . the first known explicit identification of part of the Americas as a continent like the other three.
Within a few years, the name "New World" began appearing as a name for South America on world maps, such as the Oliveriana (Pesaro) map of around 1504–1505. Maps of this time, though, still showed North America connected to Asia and showed South America as a separate land.
In 1507 Martin Waldseemüller published a world map, Universalis Cosmographia, which was the first to show North and South America as separate from Asia and surrounded by water. A small inset map above the main map explicitly showed for the first time the Americas being east of Asia and separated from Asia by an ocean, as opposed to just placing the Americas on the left end of the map and Asia on the right end. In the accompanying book Cosmographiae Introductio, Waldseemüller noted that the earth is divided into four parts, Europe, Asia, Africa, and the fourth part, which he named "America" after Amerigo Vespucci's first name.Zerubavel, Eviatar (2003). Terra Cognita: The Mental Discovery of America. New Brunswick: Transaction Publishers, pp. 80–82. . On the map, the word "America" was placed on part of South America.
In regard to the above-quoted verses, it is commonly accepted that there are Seven Continents or 'regions of the earth'. A. Glucklich adds that 'In the Matsya Purana, for instance, there is a seven-part map of the world ... it one centre, where an immense mountain – Mount Meru (or Maha Meru, Great Meru) – stands ... The continents encircle the mountain in seven concentric circles ... It seems clear that the Himalayas were the approximate location of Mt. Meru and the text is clear that the earth has seven continents.
based on voyages by Abel Tasman and Willem Jansz, this image shows a French edition of 1663]]From the late 18th century, some geographers started to regard North America and South America as two parts of the world, making five parts in total. Overall though, the fourfold division prevailed well into the 19th century.
Europeans discovered Australia in 1606, but for some time it was taken as part of Asia. By the late 18th century, some geographers considered it a continent in its own right, making it the sixth (or fifth for those still taking America as a single continent). In 1813, Samuel Butler wrote of Australia as "New Holland, an immense island, which some geographers dignify with the appellation of another continent" and the Oxford English Dictionary was just as equivocal some decades later."continent n. 5. a." (1989) Oxford English Dictionary, 2nd edition. Oxford University Press. "the great island of Australia is sometimes reckoned as another continent" It was in the 1950s that the concept of Oceania as a "great division" of the world was replaced by the concept of Australia as a continent.: "...the 1950s... was also the period when... Oceania as a "great division" was replaced by Australia as a continent along with a series of isolated and continentally attached islands. Footnote"
Antarctica was sighted in 1820 during the First Russian Antarctic Expedition and described as a continent by Charles Wilkes on the United States Exploring Expedition in 1838, the last continent identified, although a great "Antarctic" (Antipodes) landmass had been Terra Australis for millennia. An 1849 atlas labelled Antarctica as a continent but few atlases did so until after World War II.
Over time, the western concept of dividing the world into continents spread globally, replacing conceptions in other areas of the world. The idea of continents continued to become imbued with cultural and political meaning. In the 19th century during the Meiji period, Japanese leaders began to self-identify with the concept of being Asian, and renew relations with other "Asian" countries while conceiving of the idea of Asian solidarity against western countries. This conception of an Asian identity, as well as the idea of Asian solidarity, was later taken up by others in the region, such as Republican China and Vietnam.
From the mid-19th century, atlases published in the United States more commonly treated North and South America as separate continents, while atlases published in Europe usually considered them one continent. However, it was still not uncommon for American atlases to treat them as one continent up until World War II. From the 1950s, most U.S. geographers divided the Americas into two continents. With the addition of Antarctica, this made the seven-continent model. However, this division of the Americas did not appeal to , who saw their region spanning an América as a single landmass, and there the conception of six continents remains popular.
Some geographers regard Europe and Asia together as a single continent, dubbed Eurasia. In this model, the world is divided into six continents, with North America and South America considered separate continents.
Some geologists restrict the term continent to portions of the crust built around stable regions called . Cratons have largely been unaffected by mountain-building events (orogeny) since the Precambrian. A craton typically consists of a continental shield surrounded by a continental platform. The shield is a region where ancient crystalline basement rock (typically 1.5 to 3.8 billion years old) is widely exposed at the surface. The platform surrounding the shield is also composed of ancient basement rock, but with a cover of younger sedimentary rock. The continents are accretionary crustal "rafts" that, 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.
The margins of geologic continents are either active or passive margin. An active margin is characterised by mountain building, either through a continent-on continent collision or a subduction zone. Continents grow by accreting lighter volcanic island chains and microcontinents along these active margins, forming Orogenic belt. At a passive margin, the continental crust is stretched thin by extension to form a continental shelf, which tapers off with a gradual slope covered in sediment, connecting it directly to the oceanic crust beyond. Most passive margins eventually transition into active margins: where the oceanic plate becomes too heavy due to cooling, it disconnects from the continental crust, and starts subducting below it, forming a new subduction zone.
There are many microcontinents, or continental fragments, that are built of continental crust but do not contain a craton. Some of these are fragments of Gondwana or other ancient cratonic continents: Zealandia, which includes New Zealand and New Caledonia; Madagascar; the northern Mascarene Plateau, which includes the Seychelles. Other islands, such as several in the Caribbean Sea, are composed largely of granitic rock as well, but all continents contain both granitic and basaltic crust, and there is no clear boundary as to which islands would be considered microcontinents under such a definition. The Kerguelen Plateau, for example, is largely volcanic, but is associated with the breakup of Gondwanaland and is considered a microcontinent, whereas volcanic Iceland and Hawaiian Islands are not. The British Isles, Sri Lanka, Borneo, and Newfoundland were on the margins of the continent—only separated from the main continental landmass by inland seas flooding its margins.
The movement of plates has caused the continual formation and breakup of continents, and occasionally supercontinents, in a process called the Wilson Cycle. The supercontinent Columbia or Nuna formed during a period of 2.0–1.8 billion years ago and broke up about 1.5–1.3 billion years ago. The supercontinent Rodinia is thought to have formed about 1 billion years ago and to have embodied most or all of Earth's continents, and broken up into eight continents around 600 million years ago. The eight continents later reassembled into another supercontinent called Pangaea; Pangaea broke up into Laurasia (which became North America and Eurasia) and Gondwana (which became the remaining continents).
Beyond four continents
The Sanskrit text Rig Veda often dated 1500 BCE has the earliest mention of seven continents in the Earth, the text claims that the Earth has seven continents and Lord Vishnu Measured the entire universe from his first foot from the land of Earth which has 7 continents.
(1997). 9780520207431, University of California Press. ISBN 9780520207431
Geology
Geologists use the term continent in a different manner from geographers. In geology, a continent is defined by continental crust, which is a platform of metamorphic rock and igneous rock rocks, largely of granite 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 platforms surrounded by deep ocean basins.
Criticism
Some academics, such as the historical geographer Martin W. Lewis, argue that the systems we understand today are more rooted in social, political, and cultural history than in geological fact, a view particularly outlined in his book The Myth of Continents: A Critique of Metageography.
See also
Notes
Bibliography
External links
target="_blank" rel="nofollow"> Lost continent revealed in new reconstruction of geologic history
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