Download Lesson 2 What Are the Characteristics of the Ocean? Fast Fact

Lesson 2
What Are the Characteristics of the Ocean?
Fast Fact
Shallow and Deep Waters Light blue water around this island indicates that the water is
shallow. As the water gets deeper, it looks darker because less and less sunlight reflects
back from the bottom. In the deepest parts of the ocean, the bottom is more than 11,000 m
(36,000 ft) down! In the Investigate, you'll model some features of the ocean floor.
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Mapping the Ocean Floor
Materials
 scissors
 poster board
 shoe box with lid
 tape
 chopstick
 metric ruler
 cm graph paper
Procedure
1. Cut a strip of poster board about 11 times as long as the shoe box but just wide enough to fit
into it. Fold the strip to make a model of an ocean floor. It can show mountains, plains,
slopes, and canyons. Trim your model so that it fits into the shoe box. Tape the ends in
place.
2. Cut a slit about 0.5 cm wide along the center length of the lid. Then tape the lid to the box.
3. Trade models with another group. Do not open the lid on the model you get.
4. Plan a way to use the chopstick and the ruler to measure the depth of the ocean floor at
different places in the model. Collect the data you need to make a cross-section drawing.
On the graph paper, draw a cross section that shows the shape of the ocean floor as it would
look from the side.
5. Now open the lid of the box, and compare your drawing with the actual model.
Draw Conclusions
1. How did you use the materials to measure the depth of the ocean floor in the model?
2. What measurements did you need in order to model the ocean floor in the box?
3. Inquiry Skill How did you interpret the data to draw the side view of the ocean floor?
Investigate Further
Suppose you want to map the bottom of a lake. Plan an investigation to do this that uses
simple equipment and a small boat. What steps would you take?
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VOCABULARY
continental shelf p. 220
continental slope p. 220
abyssal plain p. 221
currents p. 222
SCIENCE CONCEPTS
 what the features of the ocean floor are like
 how the ocean affects climate
READING FOCUS SKILL
MAIN IDEA AND DETAILS Look for details about the ocean floor, ocean currents, and
ocean resources.
The Ocean Floor
As you walk from the beach into the ocean, the water gradually gets deeper and deeper. You
may think that the ocean floor continues to gradually slope downward until its surface is
smooth and flat. But this is only partly true. In reality, the ocean floor is just as varied as
the land above water. There are towering mountains, deep valleys, wide plains, and other
features. However, even with all of this variety, all ocean floors across the world can be
divided into three major regions.
The first region is the continental shelf. The continental shelf is a gradually sloping portion of
the ocean floor that is made of continental crust. When you wade into the ocean at the
beach, you are walking along the continental shelf. In some places, the continental shelf
extends into the ocean as little as 30 km (19 mi) from the coast. The continental shelf
comes to an end at the edge of the continental slope. The continental slope is found at the
border between continental crust and oceanic crust. Parts of the "slope" are actually more
like
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cliffs as it plunges down steeply to the deep- ocean floor. The average depth of the ocean is
3720 m (12,200 ft). However, there are some areas that are much deeper.
At the end of the continental slope, the ocean floor gradually flattens out into the abyssal
(uh•BIS•uhl) plain. The abyssal plain is the vast floor of the deep ocean. This part of the
ocean covers almost half of Earth's surface. A layer of thick sediment covers the abyssal
plain. This makes it the flattest place on Earth. But this flat plain is not without features.
That's because the abyssal plain is broken up by deep trenches, ridges, and mountains. In
fact, some of the world's highest mountains and deepest canyons lie beneath the ocean's
surface. Many of these landforms are found along the mid-ocean ridges. Here, the tectonic
plates of Earth's crust are being split apart. As the plates are pulled apart, molten rock
pushes up from below. It forms new ocean floor and a vast mountain range. Where two
oceanic plates run into each other, the dense ocean crust sinks down into Earth's mantle,
rolling under like a conveyor belt, to form a deep-ocean trench. Such trenches are the
deepest parts of the ocean. Some of them plunge more than 10,000 m (33,000 ft) below the
surface. The Mariana Trench in the Western Pacific is 11,033 m (36,198 ft) deep.
MAIN IDEA AND DETAILS What are the three main regions of the ocean floor?
---see pictures pg.220
A continental shelf rings each continent. At the edge of the continental shelf is the shelf
break where the continental slope begins.
The continental slope is the edge of the continent. The ocean floor drops, on average,
about 70 m (230 ft) for every kilometer of width.
---see diagram
This diagram shows the continental shelf and slope off the edge of the East Coast of the
United States.
---see pictures pg.221
This shelf break off the coast of California marks the border between the North American
continental shelf and the continental slope.
High ridges and deep trenches form where the rocky plates of Earth's crust meet.
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How Oceans Affect Climate
Oceans cover nearly three-fourths of Earth's surface. Because of this, oceans have important
effects on Earth's climate. In fact, without oceans, Earth's climate would be too harsh to
support life. This is because water takes much longer to heat up and cool down than land
does. Because water takes longer to heat up, it helps keep land cooler during the summer.
And because water takes longer to cool down, it helps keep land warmer during the winter.
This is why seasons are more extreme in the middle of continents.
The differences in water temperatures and land temperatures also cause winds to form. During
the day, land temperatures rise faster than water temperatures. As the air warms, it
becomes less dense. The denser, cooler air over the ocean moves toward the land and the
warm air moves upward. This is how a sea breeze forms. The air on land stays cooler
during the day because of the sea breeze. The opposite situation occurs at night. The land
cools down more quickly than the ocean water. The warmer air over the ocean moves
upward and the cooler air over land moves in to take its place. This movement of air is
called a land breeze.
Earth's oceans also affect climate in another way. Suppose you placed a beach ball in the
middle of the ocean. Even if there was no wind, would the ball stay in that same spot?
Probably not. That's because ocean water flows in steady, streamlike movements known as
currents. Currents are caused by many factors, including wind, gravity, heating from the
sun, and Earth's rotation.
Surface currents, or currents near the surface of the ocean, are produced by global winds.
Global winds move in fairly regular patterns, so surface currents also move in regular
patterns. The movements of surface
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currents are predictable. The temperatures of surface currents are also predictable. Warmwater currents, such as the Gulf Stream, begin in tropical regions. The Gulf Stream flows
northeast from the Caribbean Sea. It carries warm water across the North Atlantic toward
Europe. During the winter, the warm Gulf Stream helps keep Europe's climate mild.
Currents can also cause warm climates to cool down. Cool-water currents, such as the
California Current, form near the poles and flow toward the equator. The California
Current flows southward down the West Coast of the United States. The current helps keep
summers along the West Coast cool. The current also keeps the ocean water on the West
Coast much cooler than the ocean water on the East Coast of the United States.
MAIN IDEA AND DETAILS How does the ocean help keep Earth's climate mild?
Insta-Lab
Heating Things Up
Fill a paper cup with water. Leave a second cup empty. Place a thermometer in each cup.
Record the temperatures in both cups. Set both cups under a lamp with a 100-W bulb. Turn
the lamp on. Record the temperatures in both cups every 5 minutes for 15 minutes. Turn
the lamp off. After 5 minutes, record the temperatures of both cups. Graph your data to
show how the temperatures in the two cups changed over time. Which heated up and
cooled down faster—air or water?
---see pictures pg.222
By following the arrows, you can see how currents flow across the surface of the ocean.
This map shows some of Earth's major surface currents.
This is what ocean currents look like when satellite data is analyzed.
---see picture pg.223
This California surfer must wear a wet suit to stay warm because the California Current
carries cool water down the West Coast of the United States.
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Ocean Exploration
There are many obstacles that hinder the exploration of Earth's oceans. Pressure increases
greatly as you descend below the surface. The ocean depths are also cold and dark. Despite
these obstacles, scientists have found ways to explore oceans.
In the early 1900s, researchers developed sonar, which stands for sound, navigation, and
ranging. Sonar systems send out sound waves to locate objects underwater. Sound waves
bounce off objects and back to the sonar equipment. The same thing happens when your
voice echoes in a large room.
If you have ever been swimming, you know how long you can hold your breath. Imagine trying
to study a coral reef if you had to return to the surface every few minutes for a breath.
Scuba gear enables scientists to spend longer periods of time underwater. Scuba divers
carry tanks of oxygen on their backs and can stay underwater until their tanks are empty.
The great pressure in the ocean limits how deep a person with scuba gear can dive. Underwater
robots have been developed to travel to the deepest parts of the ocean. The robots are
controlled remotely. Lights and a camera enable researchers to see where the robot is
diving. Other data collection instruments can be attached to a robot.
Recently, miniature submarines, or minisubs, have been developed to carry people even deeper
into the ocean. Using the minisubs, scientists have discovered many new species living
deep below the ocean's surface. Often, the submarines have robotic arms that allow
researchers to collect items from the ocean floor.
MAIN IDEA AND DETAILS What are four technological advances that scientists use to
study the oceans?
---see pictures
This researcher is using scuba gear to study underwater plants.
This robot is being used to study coral reefs.
Scientists can use sonar to track the movements of whales.
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Reading Review
1. MAIN IDEA AND DETAILS Draw and complete the graphic organizer.
2. SUMMARIZE Write a short paragraph summarizing various ways people use the ocean.
3. DRAW CONCLUSIONS Ships often use currents to cut their travel time from one place to
another. Where might ships travel to by using the Gulf Stream?
4. VOCABULARY Write a short paragraph using vocabulary terms from this lesson to
describe what the ocean floor is like.
Test Prep
5. Critical Thinking At the beach, you notice a strong breeze blowing in from the water.
Explain how this breeze is formed.
6. If Earth had no oceans, how would the temperatures on Earth change?
A. They would be higher.
B. They would be lower.
C. They would be milder.
D. They would be more extreme.
Writing
Expository Writing
Research a scientist whose work was closely related to oceans. Examples include Jacques
Cousteau, William Beebe, and Thor Heyerdahl. Write an essay explaining their
contributions to the field of oceanography. Present your essay to the class.
Math
Solve Problems
Sound travels through seawater at about 1500 m/sec (4921 ft/sec). A ship sends out a sonar
pulse that takes 4 sec to travel to the ocean floor and back. How deep is the ocean at that
point? How deep would it be if the pulse took only 1 sec?
Literature
Books Set at Sea
Many great pieces of literature, such as Moby Dick and 20,000 Leagues Under the Sea, are set
at sea. Read a book, short story, or poem in which the story takes place at sea. Write a
report about the story, giving special attention to the story's setting.
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