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Chapter 4
Plate Tectonics
Review
Choose the best response. Write the letter of that choice in the space provided.
1. The German scientist Alfred Wegener proposed the existence of a huge landmass called
a. Panthalassa.
b. rift valley.
c. Mesosaurus.
d. Pangaea.
2. Support for Wegener’s hypothesis of continental drift includes evidence of changes in
a. climatic patterns.
c. terranes.
b. Panthalassa.
d. subduction.
3. New ocean floor is constantly being produced through the process known as
a. subduction.
c. seafloor spreading.
b. continental drift.
d. terranes.
4. An underwater mountain chain formed where new crust is created by seafloor spreading
is called a
a. divergent boundary.
c. mid-ocean ridge.
b. subduction zone.
d. convergent boundary.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
5. The term tectonics comes from a Greek word meaning
a. “movement.”
b. “plate.”
c. “continent.”
d. “construction.”
6. The layer of mantle with plastic rock that underlies the plates is called the
a. lithosphere.
b. asthenosphere. c. oceanic crust.
d. terrane.
7. To date, scientists have identified approximately
a. 5 plates.
b. 30 plates.
c. 15 plates.
d. 50 plates.
8. Two plates moving away from each other form a
a. transform boundary.
c. fracture.
b. convergent boundary.
d. divergent boundary.
9. The collision of one lithospheric plate with another forms a
a. convergent boundary.
c. rift valley.
b. transform boundary.
d. divergent boundary.
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Chapter 4
Choose the best response. Write the letter of that choice in the space provided.
10. The region along lithospheric plate boundaries where one plate is moved beneath another
is called a
a. rift valley.
c. subduction zone.
b. transform boundary.
d. convergent boundary.
11. Two plates grind past each other at a
a. transform boundary.
c. subduction zone.
b. convergent boundary.
d. divergent boundary.
12. Convection occurs because heated material becomes
a. less dense and rises.
c. more dense and sinks.
b. more dense and rises.
d. less dense and sinks.
13. Scientists think that the upwelling of mantle material at mid-ocean ridges is caused by
the motion of lithospheric plates and comes from
a. the lithosphere.
c. terranes.
b. the asthenosphere.
d. rift valleys.
14. The parts of the continents that are made up of formerly separate pieces of lithosphere
are called
b. plates.
d. oceanic crust.
Critical Thinking
Read each question or statement and answer it in the space provided.
1. In what ways might the concept of continental drift be compared to a jigsaw puzzle?
14
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a. terranes.
c. continental crust.
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Chapter 4
Read each question or statement and answer it in the space provided.
2. If Alfred Wegener had found identical fossil remains of plants and animals that had lived no
more than 10 million years ago in both eastern Brazil and western Africa, what might he have
concluded about the breakup of Pangaea?
Copyright © by Holt, Rinehart and Winston. All rights reserved.
3. Assume that the total surface area of the earth is not changing. If new material is being added to
the earth’s crust at one boundary, what would you expect to find happening at another boundary?
4. Explain the following statement: Due to the process of seafloor spreading, the ocean floor is
constantly renewing itself.
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Chapter 4
Application
Read each question or statement and answer it in the space provided.
1. Explain the role of technology in the progression from the hypothesis of continental drift to the
theory of plate tectonics.
2. If you wanted to prove that a microplate terrane had been scraped onto the North American
plate, what kind of evidence would you search for?
16
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3. Construct a concept map using 10 of the new terms listed on page 78 of your textbook by making connections that illustrate the relationship among the terms.
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away from the ridge, and add a different colored
pair of strips (reversed polarity) between the ridge
and the first strips. This represents crust with a different magnetic pattern. Repeat for all pairs of
strips. Emphasize that striped patterns cannot actually be seen on the seafloor but that you are using
them to illustrate the magnetic orientation of minerals in rocks. Explain that scientists do not know the
cause of the reversals in the earth’s magnetic field.
Pages 76-77: Demonstration
(Reinforcement)
Materials: two small blocks of wood, two colors of
modeling clay
To show students how terranes become part of
other landmasses, construct models of the lithosphere with the materials listed above. Use Figure
4-9 on page 77 as a model. The clay represents continental crust, and the blocks represent plates. Place
a 3 cm layer of clay on top of each block. Make sure
that this layer is the same color for each block. Add
a terrane of the second color to one block only.
Align the blocks, and then slide the block with the
terrane under the other to illustrate subduction. Ask
what happens. (The terrane is welded to the continent.) Ask students how they could tell from the
model that the terrane was not originally part of the
continent (color). Ask how geologists identify terranes. (See page 76.)
Small-Scale Investigation
Lithospheric Plate Boundaries (p. 75)
Science Process Skills: constructing models,
demonstrating, describing, explaining
Answers to Analysis and Conclusions
1. a convergent boundary
2. a transform boundary
3. With direct collisions, the edges buckle and rise;
with grinding motion, the edges become rough
and jagged. Direct collisions crumple and uplift
the earth’s crust, producing mountains. Grinding
causes the earth’s crust to fracture.
Alternative Lab: Introduction to Lithospheric Plate
Boundaries—WARD’S 34 M 1216
T40
Chapter 4
Chapter 4 Review
Answers to Review
1. d
2. a
3. c
4. c
5. d
6. b
7. b
8. d
9. a
10. c
11. a
12. a
13. b
14. a
Answers to Critical Thinking
1. According to Wegener’s hypothesis, the continents once fit together like the pieces of a jigsaw
puzzle, making up a huge landmass that Wegener
called Pangaea.
2. Wegener might have concluded that the breakup of
Pangaea occurred less than 10 million years ago.
3. an equal amount of material being subducted
4. As the ocean floor spreads, new material is added
at a mid-ocean ridge while the oldest material is
subducted at a plate boundary. The subducted
material melts and eventually rises again at the
mid-ocean ridge.
Answers to Application
1. Because the technology for ocean-floor exploration was unavailable during Wegener’s lifetime,
he was unable to offer conclusive evidence supporting his hypothesis. Not until the 1960s were
scientists able to explore the ocean floor and discover evidence of seafloor spreading and convection currents within the asthenosphere, a possible
mechanism for plate movement. This new evidence helped to explain earlier observations and
led to the theory of plate tectonics.
2. rocks, fossils, and other clues, such as the magnetic orientation of the rock, that are normally
not found on the North American plate
3. Student concept maps should connect new terms
with appropriate linking words, indicating their
understanding of the concepts in the chapter.
In-Depth Investigation
A Model of Convection Currents
(pp. 80–81)
Approximate time: 1 class period
Objectives: to demonstrate convection currents in
water; to show how convection currents in the solid
asthenosphere may be the cause of plate motion
Skills: observing, measuring, experimenting, predicting, interpreting models