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SECTION
PLATES MOVE APART.
CHAPTER 18
Plate Tectonics
18.3 Reading Study Guide A
BIG IDEA The
movement of tectonic plates causes geologic changes on Earth.
KEY CONCEPT
Plates move apart.
Vocabulary
divergent boundary occurs where tectonic plates move apart
convergent boundary occurs where tectonic plates push together
transform boundary occurs where tectonic plates scrape past each other
rift valley a gap formed between two diverging plates
magnetic reversal when Earth’s magnetic north and south poles switch places
hot spot an area of volcanic activity that develops above a plume in the mantle
Review
1.
All of the continents were not joined at one time.
2.
Continental drift explains how plates move over Earth’s surface.
Take Notes
I.
Tectonic plates have different boundaries.
3.
How are divergent boundary and rift valley related?
II. The sea floor spreads apart at divergent boundaries.
4.
What is another name for a divergent boundary in the ocean? In what
direction are tectonic plates moving at these boundaries?
A. Mid-Ocean Ridges and Rift Valleys
5.
The sketch below shows a mid-ocean ridge. Circle the place where the molten
material is rising up to form new crust. What is this place called?
34 THE CHANGING EARTH, CHAPTER 18, READING STUDY GUIDE A
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
If the statement is true, write true. If it is false, replace the underlined words to make
it true.
What is the name of the mid-ocean ridge that runs the length of the
Atlantic Ocean?
CHAPTER 18
Plate Tectonics
6.
B. Sea-Floor Rock and Magnetic Reversals
7.
Recall that Earth has a magnetic field that makes it behave like a bar magnet.
Magnetic reversals happen when
Where are magnetic reversals recorded?
III. Continents split apart at divergent boundaries.
8.
Fill in the main-idea chart for the main idea shown.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
Continents split apart at divergent boundaries.
Continents begin to split apart as
.
As a rift valley continues to grow wider, its floor
.
An example of a filled rift valley is
.
IV. Hot spots can be used to track plate movements.
9.
What is a magma plume? Why are hot spots so important?
THE CHANGING EARTH, CHAPTER 18, READING STUDY GUIDE A 35