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Afro-Eurasia, Afroeurasia,〔Field, Henry. "(The University of California African Expedition: I, Egypt )", ''American Anthropologist,'' New Series Vol. 50, No. 3, Part 1 (Jul. - Sep., 1948), pp. 479-493.〕 or Eurafrasia, known in antiquity as the Ecumene and most commonly known since the Age of Exploration as the Old World, is the largest landmass on Earth, primarily in the Northern and Eastern Hemispheres. The term is a portmanteau of its constituent parts: Africa and Eurasia, the latter conventionally divided into Europe and Asia.〔 Afro-Eurasia encompasses 84,980,532 square kilometers (32,811,166 sq mi) and has a population of approximately 6 billion people or roughly 85% of the world population.〔Based upon population estimates for 2007 cited in a UN report, ''(World Population Prospects: The 2006 Revision (Highlights) ).''〕 In geopolitical contexts, it is sometimes known as the World Island, a term coined by H.J. Mackinder.〔Mackinder, Halford John. ''The Geographical Pivot of History''.〕〔See Francis P. Sempa, (Mackinder's World )〕 == Geology == Afro-Eurasia is typically considered to comprise two or three separate continents but is not a proper supercontinent. Instead, it is the largest present part of the supercontinent cycle. The oldest part of Afro-Eurasia is probably the Kaapvaal Craton, which together with Madagascar and parts of India and western Australia formed part of the first supercontinent Vaalbara or Ur around 3 billion years ago. It has made up parts of every supercontinent since. At the breakup of Pangaea around 200 million years ago, the North American and Eurasian Plates together formed Laurasia while the African Plate remained in Gondwana, from which the Indian Plate split off. This impacted southern Asia around 50 million years ago and began the formation of the Himalayas. (Around the same time, it also fused with the Australian Plate.) The Arabian Plate broke off of Africa around 30 million years ago and impacted the Iranian Plate between 19 and 12 million years ago, ultimately forming the Alborz and Zagros chains of Iranian Plate. After this initial connection of Afro-Eurasia, the Betic corridor along the Gibraltar Arc closed a little less than 6 million years ago, fusing Northwest Africa and Iberia together. This led to the nearly-complete desiccation of the Mediterranean Basin, the Messinian salinity crisis. Eurasia and Africa were then again separated: the Zanclean Flood around 5.33 million years ago refilled the Mediterranean Sea through the Strait of Gibraltar and the Red Sea and Gulf of Suez Rifts further divided Africa from the Arabian Plate. Today, Africa is now joined to Asia only by a narrow land bridge (which has been canalized) at the Isthmus of Suez and remains separated from Europe by the Straits of Gibraltar and Sicily. Paleogeologist Ronald Blakey has described the next 15 to 100 million years of tectonic development as fairly settled and predictable.〔Manaugh, Geoff & al. ("What Did the Continents Look Like Millions of Years Ago?" ) in ''The Atlantic'' online. 23 Sept 2013. Accessed 22 July 2014.〕 In that time, Africa is expected to continue drifting northward. It will close the Strait of Gibraltar around 600,000 years from now,〔(Africa will collide with Europe and Asia, 50 Million years from now )〕 closing and quickly evaporating the Mediterranean Sea.〔"Only the inflow of Atlantic water maintains the present Mediterranean level. When that was shut off sometime between 6.5 to 6 MYBP, net evaporative loss set in at the rate of around 3,300 cubic kilometers yearly. At that rate, the 3.7 million cubic kilometres of water in the basin would dry up in scarcely more than a thousand years, leaving an extensive layer of salt some tens of meters thick and raising global sea level about 12 meters." Cloud, P. (1988). ''Oasis in space. Earth history from the beginning'', New York: W.W. Norton & Co. Inc., 440. ISBN 0-393-01952-7〕 No supercontinent will form within the settled time frame, however, and the geologic record is full of unexpected shifts in tectonic activity that make further projections "very, very speculative".〔 Three possibilities are known as Novopangaea, Amasia, and Pangaea Ultima. In the first two, the Pacific closes and Africa remains fused to Eurasia, but Eurasia itself splits as Africa and Europe spin towards the west; in the last, the trio spin eastward together as the Atlantic closes. == History == Humans evolved in Africa and spread from there throughout Europe and Asia before sailing to Oceania and crossing the Bering land bridge during the last glacial period to the Americas. On average, present-day Africans exhibit lower levels of DNA from archaic humans than Europeans and Asians, suggesting interbreeding with Neanderthals between 50 to 60,000 years ago. The long expanse of temperate climate in Eurasia and North Africa saw the birth of agriculture around 10,000 years ago, eventually leading to domesticated livestock and metallurgy. (Similar developments occurred independently in the Americas, but several millennia later.) By the late Chalcolithic, city-states had arisen in Sumeria and were followed by civilizations in other locations such as China's Yellow and Yangtze Rivers and the Subcontinent's Indus River. Major empires have included the Roman, Arabian, Mongolian, Ottoman, Russian, Japanese, and British Empires, as well as the many empires of China. The European Age of Discovery, with its attendant Columbian Exchange and colonization, began the globalization of the world's cultures. It was the cradle of the first and second Industrial Revolutions, as well as the setting of the bloodiest wars in history. The First and Second World Wars led to decolonization and Communist revolutions around the world, although the Revolutions of 1989 ended the Cold War in a victory for the Capitalist Bloc. 8 of the 9 states with nuclear weapons lie in Eurasia and current major powers include China, France, Germany, India, Japan, Russia, the United Kingdom, and the European Union. Today, Afro-Eurasia includes the vast majority of the world's peoples and cultures, as well as a majority of the world's economy. Its languages are the most- and most widely-spoken in the world, with most humans speaking either an Indo-European or Sino-Tibetan language. It was the birthplace of most religions, including the four major faiths of Christianity, Islam, Buddhism, and Hinduism, as well as empirical science, humanism, and secularism. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Afro-Eurasia」の詳細全文を読む スポンサード リンク
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