Pacific Ocean

The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the continents of Asia and Australia in the west and the Americas in the east.

At 165,250,000 square kilometers (63,800,000 square miles) in area (as defined with a southern Antarctic border), the Pacific Ocean is the largest division of the World Ocean and the hydrosphere and covers approximately 46% of Earth's water surface and about 32% of the planet's total surface area, larger than its entire land area (148,000,000 km² (57,000,000 sq mi)). The centers of both the water hemisphere and the Western Hemisphere, as well as the oceanic pole of inaccessibility, are in the Pacific Ocean. Ocean circulation (caused by the Coriolis effect) subdivides it into two largely independent volumes of water that meet at the equator, the North Pacific Ocean and the South Pacific Ocean (or more loosely the South Seas). The Pacific Ocean can also be informally divided by the International Date Line into the East Pacific and the West Pacific, which allows it to be further divided into four quadrants, namely the Northeast Pacific off the coasts of North America, the Southeast Pacific off South America, the Northwest Pacific off Far Eastern/Pacific Asia, and the Southwest Pacific around Oceania.

The Pacific Ocean's mean depth is 4,000 meters (13,000 feet). The Challenger Deep in the Mariana Trench, located in the northwestern Pacific, is the deepest known point in the world, reaching a depth of 10,928 meters (35,853 feet). The Pacific also contains the deepest point in the Southern Hemisphere, the Horizon Deep in the Tonga Trench, at 10,823 meters (35,509 feet). The third deepest point on Earth, the Sirena Deep, was also located in the Mariana Trench. It is the warmest ocean, as its temperatures can reach as high as 31°C (88°F) due to it surrounding major and minor Pacific islands, which have a tropical, hot climate.

The Pacific has many major marginal seas, including (listed clockwise from the west) the Philippine Sea, South China Sea, East China Sea, Sea of Japan, Sea of Okhotsk, Bering Sea, Gulf of Alaska, Gulf of California, Tasman Sea, and the Coral Sea.

In the early 16th century, Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and sighted the great "Southern Sea", which he named Mar del Sur (in Spanish). Afterwards, the ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1520, as he encountered favorable winds upon reaching the ocean. He called it Mar Pacífico, which in Portuguese means 'peaceful sea'.

Across the continents of Asia, Australia and the Americas, more than 25,000 islands, large and small, rise above the surface of the Pacific Ocean. Multiple islands were the shells of former active volcanoes that have lain dormant for thousands of years. Close to the equator, without vast areas of blue ocean, are a dot of atolls that have over intervals of time been formed by seamounts as a result of tiny coral islands strung in a ring within surroundings of a central lagoon.

Important human migrations occurred in the Pacific in prehistoric times. Modern humans first reached the western Pacific in the Paleolithic, at around 60,000 to 70,000 years ago. Originating from a southern coastal human migration out of Africa, they reached East Asia, Mainland Southeast Asia, the Philippines, New Guinea, and then Australia by making the sea crossing of at least 80 kilometres (50 mi) between Sundaland and Sahul. It is not known with any certainty what level of maritime technology was used by these groups – the presumption is that they used large bamboo rafts which may have been equipped with some sort of sail. The reduction in favourable winds for a crossing to Sahul after 80,000 B.P. fits with the dating of the settlement of Australia, with no later migrations in the prehistoric period. The seafaring abilities of pre-Austronesian residents of Island South-east Asia are confirmed by the settlement of Buka by 32,000 B.P. and Manus by 25,000 B.P. Journeys of 180 kilometres (110 mi) and 230 kilometres (140 mi) are involved, respectively.

The descendants of these migrations today are the Negritos, Melanesians, and Indigenous Australians. Their populations in maritime Southeast Asia, coastal New Guinea, and Island Melanesia later intermarried with the incoming Austronesian settlers from Taiwan and the northern Philippines, but also earlier groups associated with Austroasiatic-speakers, resulting in the modern peoples of Island Southeast Asia and Oceania.