Continent


A continent is any of several large terrestrial geographical regions. Continents are generally identified by convention rather than any strict criteria. A continent could be a single large landmass, a landmass and nearby islands either on or beyond its continental shelf, or a part of a larger landmass, as in the case of Asia and Europe within Eurasia. Due to these varying definitions, the number of continents varies, up to seven or as few as four. Most English-speaking countries recognize seven continents. In order from largest to smallest in area, these seven are Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Different variations with fewer continents merge some of these regions; examples of this are merging Asia and Europe into Eurasia, North America and South America into the Americas, 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". 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 that formed hundreds of millions of years ago.

Etymology

From the 16th century the English noun continent was derived from the term continent land, meaning continuous or connected land and translated from the Latin terra continens. The noun was used to mean "a connected or continuous tract of land" or mainland. It was not applied only to very large areas of land—in the 17th century, references were made to the continents of the Isle of Man, Ireland and Wales and in 1745 to Sumatra. The word continent was used in translating Greek and Latin writings about the three "parts" of the world, although in the original languages no word of exactly the same meaning as continent was used.
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 and the New." 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." However, the old idea of Europe, Asia and Africa as "parts" of the world ultimately persisted with these being regarded as separate continents.

Definitions and application

By convention, continents "are understood to be large, continuous, discrete masses of land, ideally separated by expanses of water". By this definition, all continents have to be an island of some metric. In modern schemes with five or more recognized continents, at least one pair of continents is joined by land in some fashion. The criterion "large" leads to arbitrary classification: Greenland, with a surface area of, is only considered the world's largest island, while Australia, at, is deemed the smallest continent.
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.
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.

Extent

The most restricted meaning of continent is that of a continuous 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 is used to refer to mainland Europe, excluding islands such as Great Britain, Iceland, Ireland, and Malta, while the term continent of Australia may refer to the mainland of Australia, excluding New Guinea, Tasmania, and other nearby islands. Similarly, the continental United States refers to "the 49 States located on the continent of North America, and the District of Columbia."
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 and the islands on the shelf, 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. 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.

Separation

The criterion that each continent is a discrete landmass is commonly relaxed due to historical conventions and practical use. 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". Africa and Asia are joined by the Isthmus of Suez, and North America and South America by the Isthmus of Panama. In both cases, there is no complete separation of these landmasses by water. Both of 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. This viewpoint was common in the United States until World War II, and remains prevalent in some Asian and most Latin American six-continent models.
The criterion of a discrete landmass is completely disregarded if the continuous landmass of Eurasia is classified as two separate continents. 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 ice ages, greater areas of the continental shelf were exposed as dry land, forming land bridges 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 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 landmasses in the world: Africa-Eurasia-America, Antarctica, and Australia-New Guinea.

Number

There are several ways of distinguishing the continents:
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. Outside of the English-speaking world, Oceania is generally considered a continent, while Mainland Australia is regarded as its continental landmass.