Continent

Animated, colour-coded map showing the various continents and regions. Depending on the convention and model, some continents may be consolidated or subdivided: for example, Eurasia is most often subdivided into Asia and Europe (red shades), while North and South America are sometimes recognised as one American continent (green shades).

A continent is one of several very large landmasses. As of 2015 this type of landmass is known to exist only on Earth.[1] Generally identified by convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest in area to smallest, they are: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.[2]

Geologically, the continents largely correspond to areas of continental crust that are found on the continental plates. However, some areas of continental crust are regions covered with water not usually included in the list of continents. Zealandia is one such area (see submerged continents below).

Islands are frequently grouped with a neighbouring continent to divide all the world's land into geopolitical 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 a geopolitical region called Oceania.

Definitions and application

A Dymaxion map shows land masses with minimal shape distortion.

By convention, "continents are understood to be large, continuous, discrete masses of land, ideally separated by expanses of water."[3] Several of the seven conventionally recognized continents are not discrete landmasses separated completely by water. The criterion "large" leads to arbitrary classification: Greenland, with a surface area of 2,166,086 square kilometres (836,330 sq mi) is considered the world's largest island, while Australia, at 7,617,930 square kilometres (2,941,300 sq mi) is deemed the smallest continent.

Earth's major landmasses all have coasts on a single, continuous World Ocean, which is divided into a number of principal oceanic components by the continents and various geographic criteria.[4][5]

Extent

The most restricted meaning of continent is that of a continuous[6] area of land or mainland, with the coastline and any land boundaries forming the edge of the continent. In this sense the term continental Europe (sometimes referred to in Britain as "the Continent") is used to refer to mainland Europe, excluding islands such as Great Britain, Ireland, Malta and Iceland, and the term continent of Australia may refer to the mainland of Australia, excluding Tasmania and New Guinea. Similarly, the continental United States refers to the 48 contiguous states and the District of Columbia in central North America and may include Alaska in the northwest of the continent (the two being separated by Canada), while excluding Hawaii, Puerto Rico, and Guam in the oceans.

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)[7] and the islands on the shelf (continental islands), as they are structurally part of the continent.[8]

From this perspective, the edge of the continental shelf is the true edge of the continent, as shorelines vary with changes in sea level.[9] 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.

Map of island countries: these states are often grouped geographically with a neighboring continental landmass.

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 part of Europe and Madagascar part of Africa. Extrapolating the concept to its extreme, some geographers group the Australian continental plate with other islands in the Pacific into one continent called Oceania. This divides the entire land surface of Earth into continents or quasi-continents.[10]

Separation

The ideal criterion that each continent is a discrete landmass is commonly relaxed due to historical conventions. Of the seven most globally recognized continents, only Antarctica and Australia are completely separated from other continents by the ocean. Several continents are defined not as absolutely distinct bodies but as "more or less discrete masses of land".[11] Asia and Africa are joined by the Isthmus of Suez, and North and South America by the Isthmus of Panama. In both cases, there is no complete separation of these landmasses by water (disregarding the Suez Canal and Panama Canal, which are both narrow and shallow, as well as artificial). Both these isthmuses are very narrow compared to the bulk of the landmasses they unite.

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 America or the Americas. This viewpoint was common in the United States until World War II, and remains prevalent in some Asian six-continent models.[12] This remains the more common vision in Latin American countries, Spain, Portugal, France, Italy, Greece and Hungary where they are taught as a single continent.

The criterion of a discrete landmass is completely disregarded if the continuous landmass of Eurasia is classified as two separate continents: Europe and Asia. Physiographically, Europe and South Asia are peninsulas of the Eurasian landmass. However, Europe is widely considered a continent with its comparatively large land area of 10,180,000 square kilometres (3,930,000 sq mi), while South Asia, 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 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. [...]."[13] However, for historical and cultural reasons,[which?] the view of Europe as a separate continent continues in several categorizations.[citation needed]

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. This produces a four-continent model consisting of Afro-Eurasia, America, Antarctica and Australia.

When sea levels were lower during the Pleistocene ice ages, greater areas of continental shelf were exposed as dry land, forming land bridges. At those times Australia–New Guinea was a single, continuous continent. Likewise, the Americas and Afro-Eurasia were joined by the Bering land bridge. Other islands such as Great Britain were joined to the mainlands of their continents. At that time there were just three discrete continents: Afro-Eurasia-America, Antarctica, and Australia-New Guinea.

Number

There are several ways of distinguishing the continents:

Models
Seven continents Australia not Oceania.png
Color-coded map showing the various continents. Similar shades exhibit areas that may be consolidated or subdivided.
Four continents     Afro-Eurasia    America   Antarctica   Australia [14]
Five continents   Africa    Eurasia    America   Antarctica   Australia
Six continents   Africa   Asia   Europe    America   Antarctica   Australia/Oceania [15]
Six continents   Africa    Eurasia   North America   South America   Antarctica   Australia/Oceania [16][17]
Seven continents   Africa   Asia   Europe   North America   South America   Antarctica   Australia/Oceania [17][18][19][20][21][22]

The term Oceania refers to a group of island countries and territories in the Pacific Ocean, together with the continent of Australia.[15][19] Pacific islands with ties to other continents (such as Japan, Hawaii or Easter Island) are usually grouped with those continents rather than Oceania. This term is used in several different continental models instead of Australia.