1. Find the meaning of these words in the dictionary
2. Read the text
Water covers nearly three fourths of the earth’s surface. Yet humans have explored more of the surface of the moon than they have of the floor of the ocean. The surface of the Earth is actually one huge ocean with large islands, or continents, scattered here and there. The ocean is so large that you could sail on it for weeks and not see any land. The ocean is also very deep, reaching depths of more than 10 km in some places. From space the ocean looks calm, but if you walk along a beach, you can see that the ocean is constantly in motion.
If the earth were completely smooth, its surface would be covered evenly with water to a deep of over 2,5 km. Only about 60 percent of the Northern Hemisphere is covered with water since most of the continents are found there. About 81 percent of the Southern Hemisphere is covered with water.
Oceans are major expanses of salt water with surface areas larger than 10 million km2. Even though the earth has only one large ocean, most geographers usually divide it into four oceans.
The area around the continent of Antarctica is sometimes called the Antarctic or Southern Ocean, but the Southern Ocean is really just the southernmost portion of the Atlantic, Pacific, and Indian oceans. Seasare expanses of salt water less than 3 million km2 in area.
The Caribbean Sea and the seas off eastern Asia are separated from the open ocean by island arcs. Sea water passes freely between the islands, making the saltiness of these seas close to that of the oceans. Other seas, such as Black Sea and the Baltic Sea, receive a great deal of fresh water from rivers that flow into them. Therefore, their saltiness is lover than that of the oceans. The Mediterranean Sea, on the other hand, joins the ocean only through the narrow, shallow Strait of Gibraltar.
Sea level does not remain constant and has varied considerably over the ages. Six million years ago, the passage between the Atlantic and the Mediterranean Sea closed due to the movement of Africa and the lowering of the water level in the oceans. Over the next thousand years, the Mediterranean nearly dried up. The Mediterranean remained dry for several thousand years, and then the ocean level rose again. This cycle was repeated many times over the next million years.
3. Decide where the sentences go in the text
a. Unique in the solar system, Earth is truly water planet.
b. Seas are partially enclosed by land and are therefore somewhat separated from the oceans.
c. The saltiness of the Mediterranean is higher than that of the open ocean because of a high evaporation rate.
4. Are the following statements true or false?
1. Water covers about 50% of the Earth's surface
2. The ocean looks calm from space
3. Most of the Northern Hemisphere is covered with water
4. The Earth has one large ocean that is divided into four oceans and numerous seas