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Answers to Exploration Questions: Plate Tectonics

1. Describe the plate motions along the Himalayan Mountains. Do you think these mountains are getting larger, smaller, or staying the same? Explain your answer.
ANSWER: Along the Himalayan Mountains, two plates are pushing into each other. Since both plates have continental crust at this boundary, they crumple and fold up, forming a mountain range. The plates are still moving, so the mountains continue to grow taller.
2. Given Earth’s history, do you think there will ever be another supercontinent like Pangea? Explain your answer.
ANSWER: Over Earth’s 4.5 billion year history, the continents have come together and spread apart at least three times. This motion is driven by convection in Earth’s mantle. Since Earth’s mantle will continue to flow, the plates will continue to move. Given Earth’s history and the flow of the mantle, it is likely that there will be another supercontinent like Pangea.
3. Write a caption for this map.
ANSWER: The Pacific plate is sinking beneath the North American plate, forming a subduction zone along the plate boundary shown as the red line with triangles. The sinking Pacific plate causes the mantle above it to melt and form magma, which rises to form the Aleutian island arc, a chain of volcanoes shown as red triangles.
4. Provide two kinds of evidence that support the theory of plate tectonics.
ANSWER MAY INCLUDE: The shapes of continents fit together like a puzzle. The matching coastlines show where the continents broke apart. Identical rocks that formed over 200 million years ago have been found on different continents. The minerals and textures of the rocks indicate that they formed in the same place before the continents separated. Identical fossils have been found in South America and Africa. This supports the explanation that these animals lived on the same continent before it separated.
5. Explain how scientists are using seismic data to learn about the geologic activity and Earth’s interior under Yellowstone National Park. (Hint: Describe how the speed of seismic waves relates to temperature in the mantle.)
         © USGS, © INEEL
ANSWER: Using seismic data, scientists can see where seismic waves move faster and slower. Since the speed of waves increases with temperature, scientists can identify areas in the mantle that are hotter and cooler and build three-dimensional models of the temperature in the mantle. These models show that Yellowstone is over a hotspot—where a column of hot material is rising from deep in the mantle.

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