The great body of water embracing the continents of the Earth is also known as the world ocean. Its major subdivisions are the Pacific, the Atlantic, the Indian, and the Arctic oceans. Some people divide the world ocean into the North Pacific, South Pacific, North Atlantic, South Atlantic, Indian, Arctic, and Antarctic - a total of seven. The term seven seas, however, originated with medieval Arabic geographers who knew only the waters of Europe and Asia.

Around the borders of the oceans lie partially enclosed seas and gulfs, such as the Mediterranean, Caribbean, Baltic, Black, Red, and North seas, the Gulf of Mexico, and the Persian Gulf. The landlocked Caspian Sea was part of a great ocean in an earlier geologic era. Gulfs are generally described as extensions of oceans or seas. The Gulf of Mexico is larger than most seas. Straits are narrow passageways connecting two large bodies of water, such as the Strait of Gibraltar between the Atlantic Ocean and the Mediterranean Sea.
Oceans, seas, gulfs, and straits cover about 71 percent of the Earth's surface. No other known planet is as watery as the Earth. The Atlantic, Pacific, Indian, and Arctic oceans cover 129,428,700 square miles. The Pacific Ocean is the largest. It occupies almost one third of the Earth's total area. The oceans are not evenly distributed over the Earth's surface. About 43 percent of their total area lies in the Northern Hemisphere and 57 percent in the Southern Hemisphere.

The word ocean is derived from Oceanus - in Greek mythology one of the Titans. He was a son of Uranus (the sky) and Gaea (the Earth), the first rulers of the world. Oceanus personified the river that the Greeks believed encircled the flat Earth.
The Pacific ocean is the world’s largest ocean - its total area is greater than the amount of dry land on Earth. The Southern Ocean circumnavigates the continent of Antarctica. It officially became an ocean in 2000, and was formed from the southern sections of the Atlantic, Indian, and Pacific oceans.
The oceans influenced the formation of the land surface of the Earth as it is known today. During several periods of the Earth's history large parts of North America were covered by the ocean. Most of the limestone, sandstone, and shale on land was deposited as sediment on the bottom of ancient, shallow seas. Chalk, such as that found in England, Texas, and Kansas, was formed on seabeds from the shells of sea creatures.

The oceans also affect climate. Water has a high capacity for storing heat. It warms more slowly than land, and it also cools more slowly. Thus the coasts of the continents have cooler summers and warmer winters than the inland areas. The influence of the Gulf Stream is one example. The oceans are also the birthplace of storms that affect climate throughout the world.
Oceans depth
Oceans currents
The largest features of the Earth's surface are the continents and ocean basins. The four major ocean basins (Arctic, Atlantic, Indian, and Pacific) are bound by landmasses and major oceanic ridges. Each continent is rimmed by a submerged, gently sloping continental margin. This includes the relatively flat continental shelf, generally found at depths of less than 600 feet (183 meters) with a width of a few miles to more than 200 miles (322 kilometers). At the shelf break portion of the margin, there is a rise in the continental shelf before the continental slope begins its plunge to the deep-sea bottom. Deep submarine canyons frequently cut into the continental margin.
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