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The islands of New Guinea, New Zealand, and Hawaii constitute 93 percent of the land area, while the remaining thousands of islands have a total land area of 89,339 sq km (34,494 sq mi), slightly less than the American state of Indiana. New Guinea, shared by the Indonesian province of Papua (formerly Irian Jaya) and the nation of Papua New Guinea, is the second largest island in the world, after Greenland. New Zealand's South Island and North Island, Oceania's next largest islands, are the world's 12th and 14th largest islands, respectively.
 Map Pacific Oceania is sometimes defined to include Australia, but because of Australia's continental size and its distinct geography, climate, and cultures it is more often considered a separate region of the world. Similarly, the Philippine, Indonesian, and Japanese archipelagos, which border Melanesia and Micronesia, bear a greater resemblance to the rest of Asia than the Pacific Islands do. Other, smaller island groups on the far northern and eastern edges of the Pacific (for example, the Aleutian Islands of Alaska and the Galapagos Islands of Ecuador) are usually classified with the nearby regions of the Western Hemisphere.
 Pacific With the exception of New Zealand and Easter Island, the Pacific Islands lie within the rainy tropics or the humid subtropics. In such areas there are no abrupt seasonal changes as occur in regions of temperate climate. Temperatures typically average close to 27 C (80 F) most of the year. At higher elevations, temperatures typically drop at the rate of 1.7 C (3 F) for every rise in elevation of 300 m (1000 ft). In parts of the central and western Pacific, monsoon climates prevail. In monsoon climates, moisture-bearing winds reverse direction once a year, creating a distinct wet season and a dry season. Because of monsoon conditions and differences in elevation, amount of rainfall, seasonal and annual, varies greatly from island to island and even on different parts of larger islands. The windward (usually eastern) slopes of the high islands sometimes receive as much as 6400 mm (250 in) of rainfall annually. The leeward (usually western) slopes of these islands are relatively dry. Many coral islands are arid or semiarid because little moisture falls as air masses pass over low-lying elevations. In recent years, most notably in the early 1980s and late 1990s, an oceanic and atmospheric phenomenon called El Nino brought great aridity to parts of the Pacific Ocean.
The Pacific Islands were first settled by migrants from Southeast Asia. Although researchers do not know exactly when these migrations began, it is clear they took place sometime in the last ice age, during the Pleistocene Epoch (which ended 10,000 years ago). During the ice age, ocean levels were much lower than they are now, exposing the Sunda Shelf and the Sahul Shelf-continental shelves, or extensions of continents that lie only a few hundred meters beneath the surface of the ocean. The Sunda Shelf is an extension of the coastal shelf of Southeast Asia and includes many of the islands of western Indonesia, such as Java and Sumatra. The Sahul Shelf is an extension of the coastal shelf of Australia and includes New Guinea and the Aru Islands of Indonesia. When the Sunda and Sahul shelves were exposed, New Guinea was attached to Australia and to Indonesia's easternmost islands by a land bridge, although it was separated from Indonesia's central islands by water. Dark-skinned peoples, ancestors to the Australoids, sailed in early boats to New Guinea and other islands of Melanesia. Tests using radiocarbon dating on sites in the Bismarck Archipelago, near Papua New Guinea, show this group reached the area at least 30,000 years ago.
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