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Geosciences LibreTexts

5.8: Earth’s Changing Surface

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  • Geologists know that Wegener was right because the movements of continents explain so much about the geology we see. Most of the geologic activity that we see on the planet today is because of the interactions of the moving plates.In the map of North America, where are the mountain ranges located? Using what you have learned about plate tectonics, try to answer the following questions:

    1. What is the geologic origin of the Cascades Range? The Cascades are a chain of volcanoes in the Pacific Northwest. They are not labelled on the diagram but they lie between the Sierra Nevada and the Coastal Range.
    2. What is the geologic origin of the Sierra Nevada? (Hint: These mountains are made of granitic intrusions.)
    3. What is the geologic origin of the Appalachian Mountains along the Eastern US?

    Remember that Wegener used the similarity of the mountains on the west and east sides of the Atlantic as evidence for his continental drift hypothesis. The Appalachian mountains formed at a convergent plate boundary as Pangaea came together.

    Before Pangaea came together, the continents were separated by an ocean where the Atlantic is now. The proto-Atlantic ocean shrank as the Pacific ocean grew. Currently, the Pacific is shrinking as the Atlantic is growing. This supercontinent cycle is responsible for most of the geologic features that we see and many more that are long gone.

    This animation shows the movement of continents over the past 600 million years beginning with the breakup of Rodinia.

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