Evidence for Continental Drift Pg. 3

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Evidence for Continental Drift

Procedures (cont.):

Part II. Examining Geologic Evidence
Students will need to work in groups of three. Begin the activity by reading the following script to your students:

Welcome back to the regional meeting of the Geoscience Society.

Now we will switch roles. You have left the field of paleontology to return to your first love - rocks! You are now geologists. Some of you specialize in glaciology, some in fossiliferous sedimentary rock, and some of you are more interested in mountain building. [Have students select one of the three Rock Clue cards.] Again, you are going to travel around the world to study your area of expertise.

Open up your Rock Evidence envelope and map out the distributions just as you did with the fossils.

Again, place continent pieces on the World Map. Share your expertise with your fellow geologists by reading the Rock Clue card you have selected. Examine the distribution of geologic evidence. Do you see anything unusual? E.g., What are glaciers doing in India?

[Have the students discuss some of the "problems" with the distribution of geologic events.]

Part III - Enter Continental Drift
Let's see what happens if we add the idea of Continental Drift, proposed by Alfred Wegener.

Wegener was not the first person to see what appeared to be an interesting fit between the continents - in particular with Africa and S. America. That actually was proposed as an idea - or a hypothesis as early as 1596. So shape was an interesting line of evidence for the hypothesis that the continents were not always in the same place as they are today. In particular the unusual fit between S. American and Africa. [Demonstrate on the overhead.]

But, Wegener did not rely JUST on a single line of evidence. He also was struck by some of the paleontologic and geologic evidence at hand. First of all, the unusual distribution of Glossopteris - a large fern. What was it doing in Antarctica? How could it spread to such diverse places when its seed is too large to be carried by wind and too fragile to last a long sea voyage.

[Hand out a copy of Wegener's map to each team.]

Let's see what happesn to your fossil evidence if you move the continents into the position proposed by Wegener. [Have students place their fossil maps in the order proposed by Wegener.] Discuss what happens.

So fossils created another line of evidence. Now let's look at the geologic evidence.

Wegener also noted that the distribution of glaciers did not seem to make sense.

[Have students place their geologic maps in the order proposed by Wegener.]

So geology provided a third line of evidence.

Even still, Wegener's views were not widely accepted. He died in the 1930s before still more fossil and geologic evidence was found to support his ideas. What Wegener was missing was the mechanism!

NOTE: This activity is an excellent portrayal of how science works. Scientists work to explain natural events by natural causes. They propose testable hypotheses and present their finding to their peers for review. Thus science is a work in progress and it is self-correcting.

The activity also provides a nice introduction for the theory of plate tectonics.

For more information: The Story of Alfred Lothar Wegener

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updated January 28, 2002