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During the 1800s, geologists were unsure what caused the creation of mountains. In 1908, an American geologist, F. B. Taylor, suggested that collisions between drifting continental plates might be the cause.
Geologists had long considered the possibility that continental plates moved � the idea of continental drift. A key piece of evidence for that theory was the amazingly similar shapes of the eastern coastline of the Americas and the western coastline of Africa and Europe. Perhaps these continents were once connected?
The discovery of the mid-Atlantic ridge provided the proof that geologists needed. This ridge runs the entire length of the Atlantic Ocean, paralleling the eastern coasts of the Americas and the western coasts of Africa and Europe. It is now accepted that molten material from deep within the Earth rises up in these locations and forces the lithosphere (hard outer crust of the Earth) outward, pushing the continents apart. This discovery led to a theory called plate tectonics, describing continental drift and its causes.
Exploring Plate Movement
In this activity, you will explore the interactions that occur between the Earth's plates at their boundaries.
1. In the Gizmotm, select BOUNDARY A. Click on Boundary name and Show labels. The diagram in the middle of this Gizmo shows a cross-section of a region, shown from the side. The colored stripe with four arrows on it, just above the sky in the diagram, is an overhead view of the same region.
1. When the BOUNDARY A tab is selected, you have control over the leftmost plate in the diagram. (Notice the boundary shown as a thin vertical black line in the ground between the two houses.) What is the name for this type of boundary?
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2. The two arrows below the BOUNDARY A tab move the plate. Click the left-hand arrow twice. Examine both the top and side views of the region and. Describe how the plate moved.
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3. Click on Show location. The red lines in the map indicate where transform boundaries are found. Where in the United States do you find this type of boundaries?
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4. Transform boundaries are often responsible for earthquakes. How does this agree with what you know about the regions shown in the map?
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2. With all of the other options still turned on, select the BOUNDARY B tab.
1. What is the name of this type of boundary?
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2. Click several times on the left-hand arrow below the BOUNDARY B tab. Describe what happens.
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Did only one plate move to cause the collision or did both plates move?
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3. What is the effect of this collision on the surface of the Earth?
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4. In what regions of the world are there currently collisional boundaries?
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Notice that one place where there are collisional boundaries is southern Asia, north of India. This region is home to the highest mountains in the world, which are the result of colliding plates. What is the name of this mountain range?
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3. Select the BOUNDARY C tab.
1. What is the name of this type of boundary?
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2. Click several times on the left-hand arrow below the BOUNDARY C tab. Describe the effects of this type of interaction between plates.
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3. In what regions of the world are these interactions taking place?
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Convergent boundaries like these commonly lead to volcanic activity. They are the cause for the so-called Pacific Ring of Fire, the volcanic regions that line the western coast of the Americas and eastern Asia. Also, the locations where one plate slides beneath another are among the deepest points in the ocean.
4. Select the BOUNDARY D tab.
1. What is the name of this type of boundary?
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What appears to be escaping from deep within the Earth at this boundary?
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2. Click several times on the right-hand arrow below the BOUNDARY D tab. Describe what occurs at this boundary.
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3. Where on the Earth are divergent boundaries found?
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How do the events that occur at a divergent boundary affect the surrounding lithosphere?
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Divergent boundaries are the cause of the sea floor spreading, the driving force behind continental drift.