THE OCEAN FLOOR

Almost three-fourths of the earth is under the ocean. Until recently, people didn't know what the ocean bottom, or floor, was like. The ocean floor is substantially different from what we thought. After World War I, scientists made a new machine. This machine told them what the bottom of the ocean was like and told how deep the ocean is in each place. For a long time, many people thought the ocean floor was flat. Now we know that there are large mountains and deep holes on the ocean floor.

There are three kinds of ocean floor under the water: the continental shelf, the continental slope, and the deep ocean floor. The continental shelf goes all around the continents. (The continents are North America, South America, Europe, Australia, Asia, Africa, and Antarctica.) The water is not more than 600 feet deep above the continental shelf. The sun can only shine down about 600 feet into the water. Plants and animals need sunshine to live so most of the fish in the ocean live above the continental shelf. The continental shelves were part of the continents many thousands of years ago. Later, the water came over them. That's why oil and minerals can be found in the continental shelf as well as in the land. Oceanographers are scientists who study the oceans. They think the continental shelves will be very important to us some day. They are trying to learn how to live and work under the water, at dephts of 500 feet or more. The continental slope begins where the continental shelf ends. At the edge of the continental shelf, the continental slope suddenly goes down two or three miles. Some continental slopes are like the side of a mountain; some are like a wall. All are very high. The largest one is five miles high, which is higher than any slope on the land. There are large canyons in the continental slopes. The canyons look like the Grand Canyon, but they are larger.

The deep ocean floor, which is the real bottom of the ocean, begins at the end of the continental slope. It is the largest and deepest of the three kinds of ocean bottom and it makes up half of all the earth's surface. Oceanographers have found a large range, or line, of mountains called the Mid-Atlantic Ridge on the ocean floor. This mountain range is 10,000 miles long. It goes through the Atlantic Ocean from Iceland to southern Africa. Many of the mountains in this range are 10,000 feet high with a mile or more of water. However, a few mountains in the Mid-Atlantic Ridge are even higher. We can see their tops above the ocean surface. The Azore Islands, near Portugal, are really the tops of some of these mountains. The Pacific Ocean has large mountains, too. The Hawaiian Islands are tops of mountains 32,000 feet high. There are some large, long holes in the ocean bottom called trenches. One of the deepest is near New Zealand. This trench is seven miles deep and is 1600 miles long and is big enough to hold six Grand Canyons. Now we know that there are mountains, canyons, and trenches under the ocean. Soon people will be able to live and work on the continental shelves. However, it will be a long time before people can reach the deep ocean floor.