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Continent

2007 Schools Wikipedia Selection. Related subjects: General Geography

   Color-coded regions of the world based on the seven commonly-recognised
   continents
   Enlarge
   Colour-coded regions of the world based on the seven
   commonly-recognised continents
   Dymaxion map by Buckminster Fuller shows land masses with minimal
   distortion as nearly one continuous continent
   Enlarge
   Dymaxion map by Buckminster Fuller shows land masses with minimal
   distortion as nearly one continuous continent
   Geographical regions used by the United Nations for statistical
   purposes
   Enlarge
   Geographical regions used by the United Nations for statistical
   purposes

   A continent is one of several large areas of land on Earth, which are
   identified by convention rather than any strict criteria. The specific
   areas of land vary, but seven areas are commonly reckoned as continents
   - they are, in order of size, Asia, Africa, North America, South
   America, Antarctica, Europe and Australia.

   Plate tectonics is the geological theory and study of the movement,
   collision and division of continents, earlier known as continental
   drift.

   The term "the Continent" (capitalized), used predominantly in the
   British Isles, means Continental Europe, that is, mainland Europe.

Definitions and application

   "Continents are understood to be large, continuous, discrete masses of
   land, ideally separated by expanses of water." However many of the
   seven most commonly recognized continents are identified by convention
   rather than adherence to the ideal criterion that each be a discrete
   landmass, separated by water from others. Likewise the criterion that
   each be a continuous landmass is often disregarded by the inclusion of
   the continental shelf and oceanic islands.

Extent of continents

   The narrowest 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 the British
   Isles, and the term continent of Australia may refer to the mainland of
   Australia, excluding Tasmania.

   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) 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. In this sense the British Isles are part of
   Europe, and Australia and the island of New Guinea together form a
   continent ( Australia-New Guinea).

   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 may be considered part of Europe and Madagascar
   part of Africa. Extrapolating the concept to its extreme, some
   geographers take Australia and all the islands of Oceania (or sometimes
   Australasia) to be equivalent to a continent, allowing the entire land
   surface of the Earth to be divided into continents or quasi continents.

Separation of continents

   The ideal criterion that each continent be a discrete landmass is
   commonly disregarded in favour of more arbitrary, historical
   conventions. Of the seven most commonly recognized continents, only
   Antarctica and Australia are separated from other continents.

   Several continents are defined not as absolutely distinct bodies but as
   "more or less discrete masses of land." Asia and Africa are joined by
   the Isthmus of Suez, and North America and South America by the Isthmus
   of Panama. Both these isthmuses are very narrow in comparison with the
   bulk of the landmasses they join.

   The division of the landmass of Eurasia into the separate continents of
   Asia and Europe is an anomaly with no basis in physical geography. The
   separation is maintained for historical and cultural reasons. An
   alternative view is that Eurasia is a single continent, one of six
   continents in total. This view is held by some geographers and is
   preferred in Russia (which spans Asia and Europe) and Eastern Europe.

   North America and South America are now treated as separate continents
   in much of Western Europe, China, and most native English-speaking
   countries. However in earlier times they were viewed as a single
   continent known as America or, to avoid ambiguity with the United
   States of America, as the Americas. They are still viewed as a single
   continent, one of six in total, in Latin America, Iberia, Italy and
   some other parts of Europe.

   When continents are defined as discrete landmasses, embracing all the
   contiguous land of a body, then Asia, Europe and Africa form a single
   continent known by various names such as Africa-Eurasia. This produces
   a four-continent model consisting of Africa-Eurasia, the Americas,
   Antarctica and Australia.

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

Number of continents

   There are several ways of distinguishing the continents.
   Models
   7 continents Antarctica

                                South America

                                North America

   Europe Asia Africa Australia
   6 continents Antarctica

                                South America

                                North America

                                   Eurasia

   Africa Australia
   6 continents Antarctica

                                   America

   Europe Asia Africa Australia
   5 continents

                                   America

   Europe Asia Africa Australia
   4 continents Antarctica

                                   America

                               Africa-Eurasia

   Australia

   The 7-continent model is usually taught in Western Europe, China, and
   most native English-speaking countries. The 6-continent
   combined-Eurasia model is preferred by the geographic community,
   Russia, Eastern Europe, and Japan. The 6-continent combined-America
   model is taught in Latin America, Iberia, Italy and some other parts of
   Europe. The 5-continent model which ignores Antarctica is the basis for
   the five rings of the Olympic symbol.

   Oceania or Australasia are sometimes used in place of Australia. For
   example, the Atlas of Canada lists 7 continents and names Oceania.

Size and population

   Continents ranked by size and population

             Size
   continent      area (km²)
   Africa-Eurasia 84 580 000
   Eurasia        54 210 000
   Asia           43 810 000
   Americas       42 330 000
   Africa         30 370 000
   North America  24 490 000
   South America  17 840 000
   Antarctica     13 720 000
   Europe         10 400 000
   Oceania        9 010 000
   Australia      8 470 000

                                           Population
                            continent      approx. population percent
                            Africa-Eurasia 5 400 000 000      86%
                            Eurasia        4 510 000 000      72%
                            Asia           3 800 000 000      60%
                            Africa         890 000 000        14%
                            Americas       886 000 000        14%
                            Europe         710 000 000        11%
                            North America  515 000 000        8%
                            South America  371 000 000        6%
                            Oceania        35 800 000         0.5%
                            Australia      24 700 000         0.3%
                            Antarctica     1 000              0.00002%

Other "continents"

   Certain parts of continents are recognized as subcontinents,
   particularly those on different tectonic plates to the rest of the
   continent. The most notable examples are the Indian subcontinent and
   the Arabian Peninsula. The large island of Greenland, though on the
   North American Plate, is sometimes referred to as a subcontinent.

   Some islands lie on sections of continental crust that have rifted and
   drifted apart from a main continental landmass. While not considered
   continents because of their relatively small size, they may be
   considered minicontinents. Madagascar, the largest example, is usually
   considered part of Africa but has been referred to as "the eighth
   continent". New Zealand and New Caledonia are island groups on
   continental crust separate from the Australia-New Guinea continental
   shelf.

History of the concept

Early concepts of the Old World continents

   The Ancient Greek geographer Strabo holding a globe showing Europa and
   Asia
   Enlarge
   The Ancient Greek geographer Strabo holding a globe showing Europa and
   Asia
   Medieval T and O map showing the three continents as domains of the
   sons of Noah - Sem (Shem), Iafeth (Japheth) and Cham (Ham)
   Enlarge
   Medieval T and O map showing the three continents as domains of the
   sons of Noah - Sem ( Shem), Iafeth ( Japheth) and Cham ( Ham)

   The first distinction between continents was made by ancient Greek
   mariners who gave the names Europe and Asia to the lands on either side
   of the waterways of the Aegean Sea, the Dardanelles strait, the Sea of
   Marmara, the Bosphorus strait and the Black Sea. The names were first
   applied just to lands near the coast and only later extended to include
   the hinterlands. But the division was only carried through to the end
   of navigable waterways. "... beyond that point the Hellenic geographers
   never succeeded in laying their finger on any inland feature in the
   physical landscape that could offer any convincing line for
   partitioning an indivisible Eurasia ...".

   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 centre of the world; Asia lay
   to the east, Europe to the west and north 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.
   Herodotus in the fifth century BC, however, objected to the unity of
   Egypt being split into Asia and Africa ("Libya") and took the boundary
   to lie along the western border of Egypt, regarding Egypt as part of
   Asia. He also queried the division into three of what is really a
   single landmass, a debate that continues nearly two and a half millenia
   later.

   Eratosthenes, in the third century BC, noted that some geographers
   divided the continents by rivers (the Nile and the Don), thus
   considering them "islands". Others divided the continents by isthmuses,
   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.

   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 take it to be the Nile or the western border of
   Egypt (Gibbon). In the Middle Ages the world was portrayed on T and O
   maps, with the T representing the waters dividing the three continents.
   By the middle of the eighteenth century, "the fashion of dividing Asia
   and Africa at the Nile, or at the Great Catabathmus [the boundary
   between Egypt and Libya] farther west, had even then scarcely passed
   away".

European discovery of the Americas

   Christopher Columbus sailed across the Atlantic Ocean to the West
   Indies in 1492, sparking a period of European exploration of the
   Americas. But despite four voyages to the Americas, Columbus never
   believed he had reached a new continent – he always thought it was part
   of Asia.

   In 1501, Amerigo Vespucci and Gonçalo Coelho attempted to sail around
   the southern end of the Asian mainland into the Indian Ocean. On
   reaching the coast of Brazil, they sailed a long way south along the
   coast of South America, confirming that this was a land of continental
   proportions and that it extended much further south than Asia was known
   to. On return to Europe, an account of the voyage, called Mundus Novus
   ("New World"), was published under Vespucci’s name in 1502 or 1503,
   although it seems that it had additions or alterations by another
   writer. Regardless of who penned the words, Mundus Novus attributed
   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", the first known explicit identification of
   part of the Americas as a continent like the other three.
   Universalis Cosmographia, Waldseemüller's 1507 world map which was the
   first to show the Americas separate from Asia
   Enlarge
   Universalis Cosmographia, Waldseemüller's 1507 world map which was the
   first to show the Americas separate from Asia

   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. On the map, the word "America" was placed on part of South
   America.

The word continent

   From the 1500s 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 1600s, references were made to the
   continents (or mainlands) of Kent, 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 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." 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.

Beyond four continents

   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.

   Antarctica was sighted in 1820 and described as a continent by Charles
   Wilkes on the United States Exploring Expedition in 1838, the last
   continent to be identified, although a great "antarctic" (antipodean)
   landmass had been anticipated for millennia. An 1849 atlas labelled
   Antarctica as a continent but few atlases did so until after World War
   II.
   The Olympic symbol of five rings representing five continents
   Enlarge
   The Olympic symbol of five rings representing five continents

   From the mid-19th century, United States atlases 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 United States atlases to treat them as one continent
   up till World War II. The Olympic symbol, devised in 1913, has five
   rings representing the five continents, with America being treated as
   one continent and Antarctica not included.

   From the 1950s, most United States geographers divided America in two
   and, with the addition of Antarctica, this made the seven-continent
   model. However, this division of America 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.

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 (typically 1.5 to
   3.8 billion years 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. 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 either a continental
   shelf and drop off to the basaltic-rock ocean basin or 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.
   The tectonic plates underlying the continents and oceans
   Enlarge
   The tectonic plates underlying the continents and oceans

   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 (the Ural Mountains) 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.

   Retrieved from " http://en.wikipedia.org/wiki/Continent"
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   with only minor checks and changes (see www.wikipedia.org for details
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