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Oceans, facts about oceans for kids

Oceans cover nearly three-quarters of the Earth's surface. Large areas of water are called oceans, and they usually separate the continents. Smaller areas separating islands or enclosed by land on several sides are called seas, gulfs or bays, channels, or straits. The waters separating Britain from the mainland of Europe are called the English Channel and the North Sea. The Gulf of Mexico and the Caribbean Sea separate North and South America from the West Indies.

In many areas, great ocean waves which are caused by the wind provide excellent opportunities for surfing: oceans - Oceans, facts about oceans for kids	View to Atlantic Ocean

There are five oceans. The Pacific Ocean, between America and Asia, is the largest and deepest, covering a third of the world's surface. It extends one-third of the way around the world at the Equator. The Atlantic Ocean (see Facts about the Atlantic Ocean) separates America from Europe and Africa. The Indian Ocean is bordered by Africa, Asia and -Australia. The Arctic Ocean lies between the land masses around the North Pole, and is covered mostly by ice. The waters around the Antarctic continent are called the Antarctic Ocean, but they do not have bordering land masses like the other oceans.

Around most coasts there is a shelf of land extending out from the coast under the sea. As a fact, this shelf, called a continental shelf, has a depth of up to 600 feet. It may extend for several hundred miles, and then the sea-floor falls steeply away to the ocean bottom or the abyss. The abyss is about 12,000 to 16,000 feet deep. It consists of great plains, called abyssal plains, crossed by ridges and mountains and by deep trenches. Islands occur where the undersea mountains, often volcanic, break the surface.

The deepest known spot on earth is the bottom of the Mindanao Trench off the Philippine Islands in the Pacific Ocean. It is 37,782 feet deep, over seven miles.

The oceans abound in life. Light penetrates the sea down to about 500 feet, and no plants can live below this depth. Thus the upper layer of the ocean and the continental shelf are rich with animal and plant life. The fish in the upper layer live down to a depth of about 2,000 feet. And below this depth, strange deep-sea fish prowl.

The ocean is constantly on the move. Waves rise and fall on the surface, caused by the wind. Waves in the open sea are rarely more than about 10 feet high, but in severe storms they may reach a height of more than 100 feet. If such waves reach the shore, they cause great damage. But the most destructive waves are the tsunamis, named after the Japanese word for great wave and often incorrectly called tidal waves. They are not caused by tides or by the wind, but by undersea earthquakes or volcanic eruptions that shake the sea-floor. Tsunamis race across the ocean at great speeds.

Ocean currents are general movements of warm and cold water throughout the world's oceans. There are several great systems of ocean currents, affecting life in the sea and the climates of bordering lands (see Ocean currents).

Oceans began as water came out of the rocks or fell from the sky as rain, when the Earth cooled from its original molten state. It filled great basins formed of heavy rock, surrounding the higher land masses of light rock. The land masses gradually moved apart, eventually forming the continents and oceans in the positions they occupy today. As rivers ran over the land into the sea, they dissolved minerals from the rock.

Man has many uses for the sea. Many people depend on fish and other sea animals for food. Useful substances such as iodine and magnesium can be extracted from salt obtained by evaporating sea water in salt pans. Other useful products from the sea include sponges and seaweeds. Trade is carried by ships across most of the world's oceans and seas. Men are beginning to harness the tides to produce electricity, and to use nuclear power to extract fresh water from sea water.

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