寻云 -
From space the earth looks like a huge water-covered globe, with a few patches of land sticking out above the water. North of the equator about 61 percent of the surface is covered by water. South of the equator 81 percent of the surface is water. Altogether more than 70 percent of the surface of our planet is covered by water.
As you study a globe, you may notice that most of the large land areas are connected, or almost so. We often speak of seven continents, but you can see that Europe, Asia, and Africa are really one landmass. South America is joined to North America, and only a narrow strait separates North America from Asia. Oceania is a separate landmass, but it is separated from Asia by very shallow water. Antarctica is about 600 miles from the tip of South America.
The largest landmass is usually divided into two "continents" along the Ural Mountains. Land to the east of the Urals is called Asia; land to the west, Europe. Asia is the largest continent, covering one third of the earth"s land area. Africa is the second largest continent. It is actually connected with Asia at the spot where the Suez Canal was dug. Oceania is the smallest continent.
The world"s coldest continent, and the most difficult to reach, is Antarctica. For centuries, people have wondered what this continent is really like, since it is covered with solid thick ice and deep snow. You may think it strange that anyone would live there. Actually a very small number of people do. They are mostly visiting scientists. A lot of research work has been carried out in recent years, but much still has to be learned about the land lying under the ice.
As we have seen, oceans cover more than 70 percent of the earth. Study of a globe shows that the oceans actually form one continuous body of water. From Antarctica, three main "gulfs" extend northward. These are called the Atlantic, Pacific and Indian Oceans. The Atlantic is longer and narrower than the other two. The Arctic Ocean is considered by some to be a northern part pf the Atlantic Ocean. The Pacific Ocean is by far the largest ocean and covers almost half of the total ocean area.
Because the ocean surface is so smooth, people may think the ocean bottom is made up of smooth plains. Actually the ocean floors are almost as irregular as the exposed land areas. Many scientists are making a study of animal and plant life in the oceans. They hope to find new resources for mankind.