Name
Date
Class
Content Vocabulary
LESSON 3
The Theory of Plate Tectonics
Directions: Each of the sentences below is false. Make the sentence true by replacing the underlined word(s)
with a term from the list below. Write your changes on the lines provided.
convection
plastic
subduction
convergent plate boundary
plate tectonics
transform plate boundary
divergent plate boundary
ridge push
lithosphere
slab pull
1. A tectonic material is something that is capable
of changing shape without breaking.
2. A transform plate boundary is one where two plates
collide.
3. Two plates separate at a convergent plate boundary.
4. Two plates slide by each other at a divergent plate
boundary.
5. The sinking of a denser plate below a more buoyant plate
is called convection.
6. Slab pull is a consequence of the rising mantle of ocean
ridges.
7. Basal drag is the force produced by the sinking of a plate.
8. Ridge push is the theory that Earth’s surface is made
of slowly moving rock plates.
9. The rigid outermost rock layer of Earth is the mantle.
10. Plate tectonics occurs when material circulates through
differences in density.
Plate Tectonics
45
Name
Date
Class
Lesson Outline
LESSON 3
The Theory of Plate Tectonics
A. The Plate Tectonics Theory
states that Earth’s surface is divided into
1. The theory of
large plates of rock. Each plate moves over Earth’s
and
changes position with respect to other plates.
a. When plates
on the seafloor, mid-ocean ridges form.
b. When one plate dives under another plate, earthquakes can result and
can form.
c. Earthquakes can also result when plates
past each
other.
2. Of all Earth’s tectonic plates, the
plate is the largest.
3. The cold, rigid rock layer on the outermost part of Earth is called the
. It consists of crust and the upper part of
the
.
4. Below the lithosphere is the
, which is so hot that it
flows like
5.
.
of lithosphere move because they rest on the flowing
asthenosphere.
B. Plate Boundaries
1. The place where two plates meet is called a(n)
.
2. When two plates move away from each other, a(n)
forms.
a. In the ocean,
are located at divergent plate
boundaries.
b. If divergent plate boundaries separate parts of a continent,
form.
3. When two plates slide by each other, a(n)
forms. This
type of movement causes
.
4. When two plates collide, a(n)
forms.
a. When plates collide, the plate that is denser slides under the less-dense plate
in the process of
46
.
Plate Tectonics
Name
Date
Class
Lesson Outline continued
b. When an oceanic plate slides under a continental plate, a deep ocean
forms. Near the trench, a line of
forms.
c. When two oceanic plates collide, a trench and a(n)
form.
d. When two continental plates collide, neither plate is subducted, and
form.
C. Evidence for Plate Tectonics
1. Scientists now use
to measure how continents move.
2. The theory of plate tectonics explains why earthquakes and
occur in certain locations.
D. Plate Motion
1. Earth’s mantle moves because warmer, less-dense materials rise and cooler, denser
materials
.
a. Materials move based on differences in their temperatures and densities in the
process of
.
b. Inside Earth,
elements provide some of the thermal
energy that causes convection.
c. Convection currents form in the mantle when thermal energy transfers from the
to the mantle.
2.
forces interact to cause tectonic plate motion.
a. Convection currents in the mantle produce a force that causes motion
called
.
b. Plates are pushed away from each other at mid-ocean ridges by the force
of
.
c. When a plate sinks below another plate, it pulls on the rest of the plate, exerting
a force called
.
E. A Theory in Progress
1. Plate tectonics is the unifying theory of
2. Plate tectonics theory is still being
.
as scientists learn
more about how Earth’s tectonic plates move.
Plate Tectonics
47
Name
Date
Content Practice A
Class
LESSON 3
The Theory of Plate Tectonics
Directions: Respond to each statement in the space provided.
1. Explain what a divergent plate boundary is.
2. Draw a diagram that shows a divergent plate
boundary.
3. Explain what a transform plate boundary is.
4. Draw a diagram that shows a transform plate
boundary.
5. Explain what a convergent plate boundary is.
6. Draw a diagram that shows a convergent
plate boundary.
Plate Tectonics
49
Name
Date
Math Skills
Class
LESSON 3
Use Proportions
A ratio is a comparison of two numbers. A ratio can be written as a fraction. Two equal
ratios can be written as a proportion. For example, 1 = 2 . When two ratios form a
2
4
proportion, the cross products are equal.
1×4=2×2
4=4
If one of the numbers in a proportion is unknown, cross multiply to solve for the unknown
number.
For example, if 2 = n4 , then
3
2n = 3 × 4
2n = 12
n=6
The Eurasian tectonic plate travels at a rate of about 0.7 cm/yr. How far will the plate travel
in 6 years?
Step 1 Use the information in the problem to write a proportion.
n cm
0.7 cm
=
1 yr
6 yr
Step 2 Cross multiply to solve for the unknown number.
0.7 × 6 = 1 × n
n = 4.2
The Eurasian tectonic plate will travel 4.2 cm in 6 years.
Practice
1. The Eurasian tectonic plate travels at a
rate of about 0.7 cm per year. How far
will the plate travel in 25 years?
2. Along the Mid-Atlantic Ridge, the
plates spread at an average rate of 5 cm
every 2 years. How far will the plates
spread in 12 years?
Plate Tectonics
3. If the mountain at a convergent plate
boundary is growing at a rate of 1.6 mm
per year, how much higher will it be in
50 years?
4. If the mountain at a convergent plate
boundary is growing at a rate of 3.6 mm
every 2 years, how long will it take for
the mountain to rise 27 mm?
53
Name
Date
School to Home
Class
LESSON 3
The Theory of Plate Tectonics
Directions: Use your textbook to answer each question or respond to each statement.
1. The lithosphere is the cold, rigid outermost rock layer of Earth.
Describe where the lithosphere is thick and where it is thin on Earth.
2. The asthenosphere is below the lithosphere. This layer is solid but very hot.
How does the asthenosphere allow tectonic plates to move?
3. Plate boundaries occur where two tectonic plates meet. The plates can
move in many different ways at the plate boundaries.
Define divergent, transform, and convergent plate boundaries.
4. Warmer rock is less dense and rises. Cooler rock is denser and sinks. The
circulation of material caused by differences in density is called convection.
Describe the three forces that cause plate motion.
54
Plate Tectonics
Name
Date
Key Concept Builder
Class
LESSON 3
The Theory of Plate Tectonics
Key Concept What is the theory of plate tectonics?
Directions: Answer each question on the lines provided.
1. What are two examples of tectonic activity?
2. Where does tectonic activity occur?
3. What causes earthquakes?
4. What forms volcanoes?
5. What forms mountains?
6. What type of tectonic activity occurs in the San Andreas Fault?
7. Where are volcanoes located in the mid-ocean ridge?
8. When they are plotted on a map, what do patterns of tectonic activity outline?
Plate Tectonics
55
Name
Date
Class
Key Concept Builder
LESSON 3
The Theory of Plate Tectonics
Key Concept What are the three types of plate boundaries?
Directions: Answer each question on the lines provided.
1. What is a plate boundary?
2. Where does a divergent
plate boundary form?
3. Where does a convergent
plate boundary form?
Directions: Put a check mark in the space that correctly identifies the type of boundary.
Plate Location
Divergent Plate
Convergent
Boundary
Plate Boundary
African Plate—South American Plate
North American Plate—Juan de Fuca Plate
African Plate—Antarctic Plate
Eurasian Plate—Philippine Plate
North American Plate—Pacific Plate
Arabian Plate—African Plate
Cocos Plate—Nazca Plate
Caribbean Plate—North American Plate
Indo-Australian Plate—Pacific Plate
56
Plate Tectonics
Name
Date
Class
Key Concept Builder
LESSON 3
The Theory of Plate Tectonics
Key Concept Why do tectonic plates move?
Directions: Identify three forces that act on plates to make them move.
1.
2.
3.
Directions: Answer each question to complete the cause-and-effect chart.
Cause
Effect
What happens when buoyant mantle
material gets near Earth’s surface?
4.
What happens as thermal energy is
transferred from the core to the mantle?
5.
How can something as massive as the
Pacific Plate move?
6.
What effect do convection currents inside
the asthenosphere have on the
lithosphere?
7.
Why do plates move away from the
mid-ocean ridges?
8.
What is the effect on a plate when a slab
sinks?
9.
What happens when tectonic plates
of different densities collide?
10.