Oceans of the world

Oceans

 "A vast area of the earth, which is covered with water is called ocean." 

Ocean

 

 

 

 

 

Arctic ocean

 A vast body of water covers the top of the world, round the North Pole. It is a body of cold water and remains frozen for months. It is called the Arctic Ocean. 

Antarctic ocean 

The Antarctic ocean surrounds the South Pole. It lies in the South of the continents of South America and Australia. It remains frozen throughout the year.

 Pacific Ocean 

The Pacific Ocean is the biggest ocean of the world, it is enclosed by the eastern coaft- of Asia and the western coasts of North and South Americas. It is very deep and boasts of the deepest trenches in the world. 

 Atlantic ocean 

The Atlantic is the second biggest ocean. It stretches from the western coasts of Europe and Africa to the eastern coasts of North and South Americas. 

Indian Ocean 

The Indian Ocean stretches from the eastern coast of Africa to the northern coast of Australia. It lies to the South of Asia.

How continents formed

 Millions of years ago, the two continents of America were part of the land mass making up Africa, Europe and Asia. Violent changes in the interior of the earth wrenched the two Americas apart and pushed them westward. A similar view has been put forward about Australia which is said to have once been a part of Asia and Africa. Geologists believe that all land masses of the world were once a compact whole, surrounded on all sides by water. By and by, wild geological forces broke up this compact mass of land into the present day continents. 
This led to the formation of seas and oceans. 

Formation of seas

The seas are very important to us as a source of food supply. Population explosion has now forced man to turn his gaze to the sea as a source of food supply. 

sea weeds and grasses

Sea-Weeds and Grasses are being used as fodder for cattle. Sea Plants are being used for medicinal purposes and for the preparation of proteins" Besides sea plants, the seas are'teeming with all kinds of fish and other marine life. The largest living creatures, the whales are found in oceans and seas. Table salt is also obtained by evaporating sea water. 
The depth of the sea is not the same every where. The .edges of the continents are covered with shallow waters, not more than 100 fathoms deep. The sea bed beneath these shallow waters is called the‘continental shelf. The slope of the continental shelf is usually gentle. In most areas the coast of a continent is bordered by mountain ranges. In some places the continental shelf is narrow and its edge lies close to the shore­line. But where the land of the continents slopes gently to the shore-line, .the gentle slope continues beneath the sea and the shelf is broad. 

 The waste of land, as a source of food for marine life:

 Much of the waste of the land brought down by rivers, is spread over the continental shelf. This waste, directly or indirectly provides food for marine life. This is one of the reasons why the world’s chief fishing grounds are found where shallow waters cover a wide continental shelf. The great banks of Newfoundland and the North Sea are the most outstanding examples.' 

The Continental Slope: 

The continental shelf, whether narrow or broad, at last dips steeply to the bed of the ocean. 
The steep slope, beyond the 600—foot line is known as the continental slope. Beyond the continental slope lies the immense expanse of the ocean floor, some kilometers deep. Very little of the silt brought down by rivers can find its way to the ocean floor. One finds scattered around are the bones of marine animals. The ocean floor contains some of the greatest known depths. 

The deepest of these lies in the Pacific, close to the Philippine Islands. The depth of this trench is about 11 km. Waves are caused by the wind in the sea. The gusts of win make the water at the surface rise and fall. The sea-water regularly rises and falls twice a day, due to gravitational pull of the moon on Earth. 

Tides  of ocean

This periodic rise and fall of the sea water is known as tides. Waves can be dangerous for boats. 

Ocean current 

 There is a constant flow of sea water along well marked paths, much like the flow of a river on land. Quite a number of such rivers keep running across the oceans of the world. They are called ocean currents. Around the Equator, the rays of the sun fall almost vertically throughout the year. They heat up and expand water of the ocean. This raises the surface of the ocean. The polar regions, on the contrary, always receive slanting rays of the sun. this keeps the ocean waters cold. The surface of the ocean gets pressed down. The immense expanse of the oceans has to keep'its level. So waters from equatorial region start flowing towards the poles. To fill up the void created by the flow, cold waters from the poles start flowing towards the Equator. Thus a network of warm currents and cold currents of ocean water comes into being. 
The currents of oceans greatly influence the human life in many ways. Ocean currents exercise a good deal of influence on the climate of many parts of the world. The global net-work of currents is a device used by nature to keep the temperature of the various seas and oceans within a limited and reasonable range. Incidentally this also helps to reduce the vigours of weather in . many parts of the world. 

Warm currents of ocean

Warm currents flowing past cold lands, make the weather mild. This is what the Gulf Stream does to the eastern coast of the United States, or the North Atlantic Drift does to England and Scandinavia. Cold currents, on the other hand, bring down the temperature of the places they pass by. The cool California Current, passing along the western coast of North America, has a cooling effect on the climate of the coast. Warm currents also help rainfall. 
They bring with them moisture laden warm air which proves a source of rainfall.

 Cold currents of ocean

 Cold currents, on the other hand, hinder rainfall. The cool air they bring with them has relatively little power to hold moisture. Such winds cannot bring1 much rain. Currents bring good type of fish with them to the warm countries. 
Currents can be of much help to ships cruising with them. The gusts of wind produce ripples on the surface of the sea. There ripples makes the water rise and fall. Generally in open seas, waves do not rise very high. But, in close seas, the waves can rise very high, especially close to the coast. 
They can be dangerously high when the sea is rough. Navigators of boats and small ships have to be very careful about stormy waves. Because these high waves can be dangerous for them.