TEACHING CLUES AND CUES
You may want to project
some of the students’
completed maps during
this discussion.
3. When they have completed both tasks, ask students if they could tell
which continent moved the most. (India) Point out that the continents
do not fit together perfectly and ask them for some possible reasons.
(Students may suggest that the scale could be wrong, the drawings
may not be quite accurate, or our measurements may be inaccurate.)
Let students discuss the possibilities. If necessary, ask if they think the
continents have always had the same outline as they do today. (No.
The sliding, colliding, and converging movement of the plates has
added new material in some places and worn the edges away in others.
Point out western North America and the place where India collided
with Asia to form the Himalayas.)
If a wall chart or map of the oceans is available, point out the conti-
nental shelves. Explain that geologically each continent extends to the
edge of its continental shelf. Does the jigsaw puzzle fit together better
if the edges of the shelves are used as continental boundaries? (Yes.)
TEACHING CLUES AND CUES
C. Conclusion
Review the steps in using magnetism to find the ancient location of the
continents. Point out to students that this evidence was not available
during Wegener’s time. In this series of activities they have
experienced some of the ways scientists established the theory of plate
tectonics. Ask:
Students will learn more
about Alfred Wegener in
the next unit, in lesson
3.2.
Q
If this information had been available, would it have helped
Wegener’s case? (Yes.)
Q
How does the last map differ from a map of today? (Discuss.)
Q
At the rate of drift (5 to 15 cm, or 2-7 inches in a year), about how
long would it take today’s continents to join into one
supercontinent? (Answers will vary.)
ADA P T A T I ON S AND E X T E N S I ON S
1. Challenge students to find out how magnetometers work and how
scientists use them, then report to the class.
2. On a map of the Pacific Ocean floor, locate the Hawaiian Islands
and the chain of islands that forms the Emperor Seamounts. Note the
sharp bend in the line of seamounts. Ask students:
Q
What could have caused the bend? (a change in the direction of
plate movement)
Q
What does this bend, and the long pattern of reversals illustrated in
the earlier activities, indicate about the possibility of the Pacific
Ocean closing? (With plates constantly changing directions, it may
not close.)
3.
Scientific American
published a series of articles on plate tectonics
in the late 1960s which were published as a collection in 1970 (see
Wilson, unit resources). Provide students with copies and ask them to
prepare a report to the class on the evolution of the theory.
A G U
/
F E M A
51
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E I S M I C
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