Download Lesson 4:

Lesson 4:
Plate Tectonics
Introduction
Watch one or more of the following videos about plate tectonics
before you read the lesson material.
http://www.youtube.com/watch?v=hwNRd1jrE0k
http://www.youtube.com/watch?v=ijWvmY0NanM
http://www.youtube.com/watch?v=ANeH9W-HMPc
Tectonic Plates and Movement
Plate tectonics is a scientific theory accepted by many geologists
that explains how the Earth’s surfaces behave. In simple terms it
means that the structure of the Earth’s outer shell is a set of plates.
For a map of the plates, go to one or more of the following websites.
http://geology.about.com/library/bl/maps/blcrustalplates.htm
http://geology.com/plate-tectonics.shtml
For a list of the plates, go to the following website.
http://geology.about.com/library/bl/blplate_size_table.htm
When you look at a map of the plates, it is obvious that the plates
don’t exactly match the continents and oceans. The continents
and ocean basins are part of the Earth’s crust, while the plates are
deeper in the Earth in the lithosphere. The plates are pieces in the
lithosphere.
Remember that the lithosphere is a solid rock layer. Right under it is
a softer, hotter layer of rock called the asthenosphere. Because of
its very hot temperatures, it can bend in a putty or taffy-like way. The
lithosphere floats on the asthenosphere so the plates are constantly
floating and changing position. This movement is very, very, very
slow—no more than a few centimeters a year.
Even though the movement is very slow, plates do move in three
different ways. In simple terms they move together, they move apart,
or they move past each other. Because of these different movements,
plates have three different kinds of boundaries or edges—
convergent, divergent and transform.
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When plates move together, they converge. As you learned in
Lesson 3, there are two kinds of crust—oceanic and continental. The
lithosphere and the plates are made of these same kinds. A plate can
be all oceanic, all continental, or part oceanic and part continental.
Therefore, when two plates converge, there are three possible types of
convergence. They are oceanic-oceanic, oceanic-continental, and
continental-continental.
During oceanic-oceanic and oceanic-continental convergence, when
the leading edges or boundaries of the plates meet, one plate moves
down. This downward movement is called subduction. Plates that are
subducted move into and through the asthenosphere into the mantle.
Some of this material gradually disappears. Some of it triggers the
formation of magma. The magma erupts, and volcanoes form.
Subduction does not happen during continental-continental
convergence because the plates are too light to be carried into the
mantle. Instead the crust buckles and crumples and is pushed upward
or sideways. Slowly over time (millions of years) the plates have been
pushed up to help form mountains like the Himalayas and the Tibetan
Plateau.
When plates move apart, they diverge. The plates are pulled apart,
not pushed apart. Divergence only happens with oceanic-oceanic
and continental-continental plates. As the plates pull apart, they are
subducted into the mantle where they partially melt and then expand
and rise. It then attaches itself to the trailing edges of the divergent
plates, causing the plate to grow. Most of these are in the ocean areas;
many of these areas are underwater.
When plates move or slide past each other, instead of moving together
or apart, they transform. Crust is neither destroyed nor created during
transformation. This is also called a transform fault. Most transform
faults are found in ocean basins. A famous land transform fault is the
San Andreas fault of California.
To review plate tectonics, go to the following website.
http://geology.about.com/library/bl/blnutshell_convergence.htm
http://geology.about.com/library/bl/maps/blplatetypeswhem.htm
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Activity 9
Plate Tectonics
with an Orange
What You Will Do:
In this activity, you will use an orange to demonstrate plate tectonics.
What You Will Need:
• oranges (one per student or one
per pair of students)
• toothpicks
• clay or play dough (optional)
What to Do:
1. For this activity pretend the
orange is the Earth and the
peel is the Earth’s crust.
2. Peel the orange in as few
pieces as possible without
using a knife.
3. The orange peel is in pieces just like the Earth’s crust. Lay the
pieces on the work surface. What do the pieces look like now?
Do they still look round or are they flatter?
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4. Use the toothpicks and try to put the peel back on the orange.
Make it fit as much as possible as it was before it was peeled.
Does the orange look as round as it did before it was peeled?
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5. The orange and its peel now look like the
Earth and its cracked crust.
6. Experiment to see if the pieces will
fit on the orange any other way.
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Activity 10
Continental Drift
What You Will Do:
In this activity, you will take notes about continental drift and make
predictions about the future.
What You Will Need:
• computer with internet access
• paper and pencil or pen
What to Do:
1. Watch at least two of the videos listed below or use a search
engine to find other websites about continental drift. As you
watch or read, take notes on the lines below or on a separate
piece of paper.
http://www.youtube.com/watch?v=GYVS_Yh6dTk&NR=1
http://www.youtube.com/watch?v=BRmvgrAeCbo
http://www.youtube.com/watch?v=nSx7ZW23uKk
2. Things I learned about continental drift.
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3. What do you think the world will look like in several million years?
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Activity 11
Chocolate Movement
What You Will Do:
In this activity, you will use chocolate to demonstrate plate movement.
What You Will Need:
• candy bar with several layers
• knife (plastic or metal)
• paper and pencil or pen
What to Do:
1. Use the knife to make two or three cracks across the middle of
the candy bar. The cracked layer is taking the role of the plates
of the lithosphere.
2. Stretch the candy bar,
pulling it apart just
a little. The exposed
caramel is similar to the
new material that rises to
form a new crust during
divergence.
3. Push the candy bar back together. Push hard
enough to form “mountains.” This is similar to what happens
during convergence.
4. Continue to push the candy bar so that one part goes under the
other part. This is similar to what happens during transform.
5. As you push and pull the candy, what happened to the top and
bottom of the candy bar? How is this similar to what happens to
the Earth? Write your thoughts below or on a separate piece of
paper.
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Review/Quiz
Plate Tectonics
Instructions: Answer the questions by filling in the circle beside the
best possible answer.
1.
The continents and ocean basin are part of the
❍ a. ionsphere
❍ b. asthenosphere
❍ c. crust
❍ d. lithosphere
2.
True or false? The plates match the continents.
❍ a. true
❍ b. false
3.
The plates are part of the
❍ a. ionsphere
❍ b. asthenosphere
❍ c. crust
❍ d. lithosphere
4.
True or false? The structure of the Earth is a series of plates.
❍ a. true
❍ b. false
5.
The lithosphere is a
❍ a. solid rock layer
❍ b. free of plates
❍ c. soft, hot layer
❍ d. none of the above
6.
The asthenosphere is
❍ a. a solid rock layer
❍ b. free of plates
❍ c. a soft, hot layer
❍ d. none of the above
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7.
True or false? The lithosphere floats on the asthenosphere.
❍ a. true
❍ b. false
8.
Plates move no more than
❍ a. a few meters a year
❍ b. a few centimeters a year
❍ c. a few feet a year
❍ d. a few kilometers a year
9.
Plates move
❍ a. together
❍ b. apart
❍ c. past
❍ d. all of the above
10. When plates move together, they
❍ a. diverge
❍ b. transform
❍ c. converge
❍ d. conform
11.
When plates move apart, they
❍ a. diverge
❍ b. transform
❍ c. converge
❍ d. conform
12. When plates move or slide past each other, they
❍ a. diverge
❍ b. transform
❍ c. converge
❍ d. conform
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