The Ocean

The earth is unusual among the planets of the Solar System in possessing a surface temperature that permits water to exist in all three states: liquid, solid and gas. The earth is also the only body in the solar system, as far as we know, to have oceans. Actually one should say “ocean”, because the Pacific, Atlantic, Indian and Arctic oceans all comprise one connected body of salt water in which the Europe-Asia-Africa mass, the American continents and smaller bodies such as Antarctica and Australia can be considered islands.

The statistics of the world ocean are impressive. It has a total area of 140 million square miles and covers more than 70 per cent of the earth's surface. It contains 98 per cent of all the H₂O on the earth and is the source of the earth’s fresh water supply as well, for 80,000 cubic miles of it are evaporated each year to fall again as rain.

The ocean is of peculiar importance to life. Almost certainly, the first forms of life originated there, and from the standpoint of sheer quantity, the oceans still contain most of our planet’s life.

And yet, until recent years mankind has been as ignorant of the oceans and particularly of the ocean floor as of another planet. Even today, astronomers know more about the surface of the moon than geologists know about the surface of the earth under the oceans.

It was once assumed that the deepest levels of the seas would be found farthest from land. But now we do know, that the deepest parts of the ocean are all near land, the Marianas Deep being the deepest of them (36,198 feet deep, south of Japan).

Volcanoes have been found by the hundreds in the deep sea, rising as cones from many parts of the ocean floor, occasionally reaching high enough to jut up above the sea level, as in the Hawaiian Islands.

Sea water is a solution of various salts, sodium chloride being the most abundant of the salts. In addition to salts, seawater contains small amounts of dissolved gases, such as oxygen and carbon dioxide. Most of this content is derived from the atmosphere and some is produced by the life present in the oceans. The natural composition of the sea has been gradually altered by the addition of man-made wastes, chemicals and pollutants of various kinds.

The oceans are a giant depository for elements, including metals, which have been brought from land by rivers and streams. Because it has been found to contain almost all the metals and other elements used by man, sea water can be considered a potential source of the metals to be needed in the future. As much as 20 billion tons of uranium, 500 million tons of silver, 10 million tons of gold, magnesium and bromine, seaweed (an important source of iodine) are contained in the oceans.