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Name<br />

The Ocean Floor<br />

By Sharon Fabian<br />

In ancient times, sailors had to<br />

be very brave to sail out across<br />

the <strong>ocean</strong> in their wooden<br />

sailing ships. They knew that<br />

the <strong>ocean</strong> was dangerous. In<br />

fact, anyone who had been a<br />

sailor for a while probably<br />

knew of someone who had<br />

sailed out, never to return.<br />

What these sailors didn't know<br />

was what caused the dangers in<br />

the <strong>ocean</strong>. They didn't know what was really out there. So sailors<br />

pictured the <strong>ocean</strong> as a bottomless pit with huge, scary sea creatures<br />

living in the deep water. Adventure stories about sailors told of ships<br />

that were sunk or wrecked when a sea monster suddenly rose up<br />

through the water.<br />

Today, we have a better picture of what it is really like under the<br />

<strong>ocean</strong>, thanks to the investigations of scientists. In the 1960s, the<br />

Navy built a deep-<strong>ocean</strong> submersible vehicle named Alvin. Alvin is a<br />

self-propelled vehicle, about eight meters long, that holds three<br />

people. It can dive to 4000 meters deep. Since that time, American<br />

and Japanese scientists have worked together to build submersibles<br />

that can go even deeper. They are working on one that will explore<br />

the deepest part of the <strong>ocean</strong>, the Challenger Deep, which is about<br />

10,000 meters below sea level.<br />

Thanks to the explorations of these sailors and scientists, we now<br />

know much more about the <strong>ocean</strong> <strong>floor</strong> than we did just 25 years ago.<br />

For one thing, we know that the <strong>ocean</strong> is not bottomless. The land<br />

continues to spread out past the continents, under the <strong>ocean</strong>s. The<br />

continental shelf is the name for the area that is under fairly shallow<br />

water at the edges of the <strong>ocean</strong>. The continental shelf has a gradual<br />

slope and is up to 1500 kilometers wide. Once you get past the<br />

continental shelf, the land drops off much more steeply. This area is<br />

called the continental slope and is only about 20 kilometers wide.<br />

Beyond the continental slope is the abyss, the deepest part of the<br />

<strong>ocean</strong>. Although the word "abyss" means a bottomless pit, the abyss is<br />

not really bottomless, just extremely deep. The abyss has mountains,<br />

plains, and valleys much like the land above water does. Underwater<br />

mountain ranges are called mid-<strong>ocean</strong> ridges. Individual mountains or<br />

volcanoes are called seamounts. Valleys are called deep-sea trenches.<br />

And the huge flat area is called the abyssal plain.<br />

In 1977, explorers began to make some amazing discoveries on the<br />

<strong>ocean</strong> <strong>floor</strong>. In their undersea submersible, they were exploring an<br />

area called the Galapagos Rift when they discovered vents that spit<br />

out very hot water and minerals. These vents are called geothermal<br />

vents, because they produce heat from within the earth. They are<br />

nicknamed "smokers."<br />

Before this, people had assumed that the bottom of the <strong>ocean</strong> was all<br />

very cold, too cold for any life to exist. The fact that no sunlight can<br />

reach the deep parts of the <strong>ocean</strong> was another reason why people<br />

believed that no life could exist there, since living things get their<br />

energy from sunlight.<br />

So, the most amazing result of this expedition was the discovery of<br />

new life forms thousands of meters below sea level. A variety of sea<br />

animals live in the deep <strong>ocean</strong>, keeping warm near the geothermal<br />

vents. Maybe even more amazing, they get their energy without the<br />

help of the sun. Bacteria here live on hydrogen-sulfide gas from the<br />

vents. The bacteria form the bottom of a food chain that includes giant<br />

clams, white crabs, and species of octopi not seen anywhere else.<br />

It's like a whole other world, under the sea.<br />

The Ocean Floor<br />

Questions<br />

1. Alvin is<br />

A. a submersible vehicle<br />

B. a sailing ship<br />

C. a type of clam<br />

D. a scientist


Name<br />

7. Explain how the creatures that live around the geothermal<br />

vents can live without sunlight.<br />

2. The gradually sloping area at the edge of the <strong>ocean</strong> is called<br />

A. the continental shelf<br />

B. the abyssal plain<br />

C. the Galapagos Rift<br />

D. the continental slope<br />

3. The area that drops off much more steeply and is only about 20<br />

meters wide is called<br />

A. the abyssal plain<br />

B. the continental slope<br />

C. the Galapagos Rift<br />

D. the continental shelf<br />

8. Why was the discovery at the Galapagos Rift such a big<br />

discovery?<br />

4. The Challenger Deep is<br />

A. the deepest part of the <strong>ocean</strong><br />

B. a song about the <strong>ocean</strong><br />

C. a book about the <strong>ocean</strong><br />

D. a submersible vehicle<br />

5. The word "abyss" means<br />

A. bottomless pit<br />

B. continental shelf<br />

C. sea monster<br />

D. plain<br />

6. "Abyss" is not really an accurate name for the deep sea bottom<br />

because<br />

A. it is not in the dictionary<br />

B. the sea is not really bottomless<br />

C. the sea is not really that deep<br />

D. it is spelled wrong

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