Download Chapter 7, Section 2 - Answer Key Directed Reading A

Answer Key
Chapter 7, Section 2: pages 198-201
Directed Reading A:
Restless Continents
Section: Restless Continents
WEGENER’S CONTINENTAL DRIFT HYPOTHESIS
D ___ 1. What hypothesis by Alfred Wegener explains why continents seem to
fit together?
a. continental spreading
c. Wegener’s puzzle
b. plate tectonics
d. continental drift
A ___ 2. According to Wegener, how many landmasses did all continents once
form?
a. one
c. seven
b. six
d. ten
C ___ 3. What did Wegener hypothesize happened to the continents?
a. They broke up and re-formed.
b. They drifted together to form a single continent.
c. They broke up and drifted to their current locations.
d. They sank into the ocean.
4. Does fossil evidence support Wegener’s theory? Explain your answer.
Wegener used fossils of the mesosaurus, a swimming reptile, and the
glossopteris, a fern, found on different sides of the Atlantic Ocean.
5. List three kinds of evidence found on both sides of the ocean that support
Wegener’s theory.
Similar fossils – on different continents
Similar rocks – same age and structure on different continents
Glacier tracks – found on different continents going in the same direction
Same ancient climatic conditions found on several continents
THE BREAKUP OF PANGAEA
6. Wegener thought that all of the present continents were once joined 245
million years ago in a landmass he called Pangaea.
7. The single landmass split into two huge continents he called Gondwana and
Laurasia about 180 million years ago.
8. When those two continents split 65 million years ago, what were formed?
 The present continents we see today in their present locations
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
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Plate Tectonics
Directed Reading A continued
SEA-FLOOR SPREADING
9. Why did many scientists reject Wegener’s hypothesis?
Scientist did not believe Wegener’s theory because he could not explain
how and why the continents moved.
10. In the process of sea-floor spreading, what happens when magma rises to
Earth’s surface and solidifies?
Sea-floor spreading is the process of adding new oceanic lithosphere
(crust) at a mid-ocean ridge (mountain chain on the ocean floor).
Match the correct definition with the correct term. Write the letter in the space
provided.
C ____ 11. process of forming new oceanic lithosphere
as magma rises to the surface
B ___ 12. areas where sea-floor spreading takes place
a.
b.
c.
d.
continental drift
mid-ocean ridges
sea-floor spreading
magnetic reversal
D ___ 13. process that happens when Earth’s
magnetic poles change place
A ___ 14. theory that explains how continents
reached their current locations
15. Rock on the ocean floor provided the final proof of sea-floor spreading with a
record of magnetic reversal.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Holt Science and Technology
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Plate Tectonics