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Plate tectonics explains many geologic phenomena, including earthquakes and some types of mountain-buildling.
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Earthquakes occur when two plates are moving against each other laterally, creating a fault line. The plates might lie motionless for decades or centuries, but enormous pressure builds along the fault line. Finally the plates snap forward, creating an earthquake. |
When two continental plates collide, neither dives beneath the other. Instead, they push each other up to form mountains. This process, called uplift, formed the Himalaya Mountains. |
For much of the twentieth century, plate tectonics was an extremely controversial
theory because it held that the continents were not stationary, but had moved
all over the globe. The German geologist Alfred Wegener first proposed that
idea (which he called Continental Drift) in 1915. What
was his evidence? 
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