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Africa is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² (11.7 million sq mi) including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people (as of 2009, see table) in 61 territories, it accounts for about 14.72% of the World's human population. The continent is surrounded by the Mediterranean Sea to the north, both the Suez Canal and the Red Sea along the Sinai Peninsula to the northeast, the Indian Ocean to the southeast, and the Atlantic Ocean to the west. Not counting the disputed territory of Western Sahara, there are 53 countries, including Madagascar and various island groups, associated with the continent.

Africa, particularly central eastern Africa, is widely regarded within the scientific community to be the origin of humans and the Hominidae tree (great apes), as evidenced by the discovery of the earliest hominids and their ancestors, as well as later ones that have been dated to around seven million years ago – including Sahelanthropus tchadensis, Australopithecus africanus, A. afarensis, Homo erectus, H. habilis and H. ergaster – with the earliest Homo sapiens (modern human) found in Ethiopia being dated to ca. 200,000 years ago.

Africa straddles the equator and encompasses numerous climate areas; it is the only continent to stretch from the northern temperate to southern temperate zones.

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Antarctica is Earth's southernmost continent, underlying the South Pole. It is situated in the Antarctic region of the southern hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean. At 14.0 million km² (5.4 million sq mi), it is the fifth-largest continent in area after Asia, Africa, North America, and South America. About 98% of Antarctica is covered by ice, which averages at least 1.6 kilometres (1.0 mi) in thickness.

Antarctica, on average, is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents. Antarctica is considered a desert, with annual precipitation of only 200 mm (8 inches) along the coast and far less inland. There are no permanent human residents but anywhere from 1,000 to 5,000 people reside throughout the year at the research stations scattered across the continent. Only cold-adapted plants and animals survive there, including penguins, seals, many types of algae, and tundra vegetation.

Although myths and speculation about a Terra Australis ("Southern Land") date back to antiquity, the first confirmed sighting of the continent is commonly accepted to have occurred in 1820 by the Russian expedition of Mikhail Lazarev and Fabian Gottlieb von Bellingshausen. The continent, however, remained largely neglected for the rest of the 19th century because of its hostile environment, lack of resources, and isolation. The first formal use of the name "Antarctica" as a continental name in the 1890s is attributed to the Scottish cartographer John George Bartholomew. The name Antarctica is the romanized version of the Greek compound word ανταρκτική (antarktiké), feminine of ανταρκτικός (antarktikos), meaning "opposite to the north".

The Antarctic Treaty was signed in 1959 by twelve countries; to date, forty-six countries have signed the treaty. The treaty prohibits military activities and mineral mining, supports scientific research, and protects the continent's ecozone. Ongoing experiments are conducted by more than 4,000 scientists of many nationalities and with different research interests.

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Asia is the world's largest and most populous continent, located in the eastern and northern hemispheres. It covers 8.6% of the earth's total surface area (or 29.9% of its land area) and with approximately 4 billion people, it hosts 60% of the world's current human population.

Asia is traditionally defined as part of the landmass of Eurasia — with the western portion of the latter occupied by Europe — located to the east of the Suez Canal, east of the Ural Mountains and south of the Caucasus Mountains (or the Kuma-Manych Depression) and the Caspian and Black Seas. It is bounded on the east by the Pacific Ocean, on the south by the Indian Ocean and on the north by the Arctic Ocean. Given its size and diversity, Asia — a toponym dating back to classical antiquity — is more a cultural concept incorporating a number of regions and peoples than a homogeneous physical entity (see Subregions of Asia, Asian people).

The wealth of Asia differs very widely among and within its regions, due to its vast size and huge range of different cultures, environments, historical ties and government systems. In terms of nominal GDP, Japan has the largest economy on the continent and the second largest in the world. In purchasing power parity terms, however, China has the largest economy in Asia and the third largest in the world.

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Australia is the smallest of the geographic continents, though not of geological continents. There is no universally accepted definition of the word "continent"; the lay definition is "One of the main continuous bodies of land on the earth's surface." (Oxford English Dictionary). By that definition, the continent of Australia includes only the Australian mainland, and not nearby islands such as Tasmania or New Guinea. From the perspective of geology or physical geography, however, a "continent" may be understood to include the continental shelf (the submerged adjacent area) and the islands on the shelf, which are taken to be structurally part of the continent. By that definition Tasmania, New Guinea and other nearby islands such as (Aru Islands and Raja Ampat Islands) are part of the Australian continent, also known as Sahul, since they are part of the same geological landmass. These islands are separated by seas overlying the continental shelf — the Arafura Sea and Torres Strait between Australia and New Guinea, and Bass Strait between mainland Australia and Tasmania.

When sea levels were lower during the Pleistocene ice age, including the last glacial maximum about 18,000 BC, the lands formed a single, continuous landmass. During the past ten thousand years, rising sea levels overflowed the lowlands and separated the continent into today's low-lying semi-arid mainland and the two mountainous islands of New Guinea and Tasmania.

Geologically, the continent extends to the edge of the continental shelf, so the now-separate lands can still be considered a continent. Due to the spread of flora and fauna across the single Pleistocene landmass, the separate lands have a related biota.

New Zealand is not on the same continental shelf and so is not part of the continent of Australia but is part of the submerged continent Zealandia. Zealandia and Australia together are part of the wider region known as Oceania or Australasia.

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Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains (or the Kuma-Manych Depression), and the Black Sea to the southeast. Europe is bordered by the Arctic Ocean and other bodies of water to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and the Black Sea and connected waterways to the southeast. Yet the borders for Europe—a concept dating back to classical antiquity—are somewhat arbitrary, as the term continent can refer to a cultural and political distinction or a physiographic one.

Europe is the world's second-smallest continent by surface area, covering about 10,180,000 square kilometres (3,930,000 sq mi) or 2% of the Earth's surface and about 6.8% of its land area. Of Europe's approximately 50 states, Russia is the largest by both area and population, while the Vatican City is the smallest. Europe is the third most populous continent after Asia and Africa, with a population of 731 million or about 11% of the world's population; however, according to the United Nations (medium estimate), Europe's share may fall to about 7% by 2050. In 1900, Europe's share of the world's population was 25%.

Europe, in particular Ancient Greece, is the birthplace of Western culture. It played a predominant role in global affairs from the 16th century onwards, especially after the beginning of colonialism. Between the 16th and 20th centuries, European nations controlled at various times the Americas, most of Africa, Oceania, and large portions of Asia. Both World Wars were ignited in Central Europe, greatly contributing to a decline in European dominance in world affairs by the mid-20th century as the United States and Soviet Union took prominence. During the Cold War Europe was divided along the Iron Curtain between NATO in the West and the Warsaw Pact in the East. European integration led to the formation of the Council of Europe and the European Union in Western Europe, both of which have been expanding eastward since the fall of the Soviet Union in 1991.

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North America is the northern continent of the Americas,[4] situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific Ocean; South America lies to the southeast. North America covers an area of about 24,709,000 square kilometers (9,540,000 square miles), about 4.8% of the planet's surface or about 16.5% of its land area. As of July 2008, its population was estimated at nearly 529 million people. It is the third-largest continent in area, following Asia and Africa, and the fourth in population after Asia, Africa, and Europe.

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South America is the southern continent of America, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. It is bordered on the west by the Pacific Ocean and on the north and east by the Atlantic Ocean; North America and the Caribbean Sea lie to the northwest.

America was named in 1507 by cartographers Martin Waldseemüller and Matthias Ringmann after Amerigo Vespucci, who was the first European to suggest that the newly discovered lands were not India, but a New World unknown to Europeans.

South America has an area of 17,840,000 square kilometers (6,890,000 sq mi), or almost 3.5% of the Earth's surface. As of 2005, its population was estimated at more than 371,090,000. South America ranks fourth in area (after Asia, Africa, and North America) and fifth in population (after Asia, Africa, Europe, and North America).