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Chapter 5: Plate Tectonics

Difficulty Level: At Grade Created by: CK-12
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But it all seems so solid!

Besides flying around on a ball of rock — orbiting a giant ball of burning gas and spinning in circles about an axis — the ground you sit on is moving! Just as Copernicus, Kepler, and Galileo had trouble convincing people that Earth orbited the Sun when it clearly seemed that Earth was at the center of the universe and everything moved around it, early adherents to the idea that continents could move had to fight against, well, common sense. Over the past century the idea that continents could move was proposed, studied, abandoned, and finally accepted.

We’ll start this concept with a field trip back in time to the scientists that developed plate tectonics theory. First, we’ll visit Wegener, and then we’ll get aboard ship to learn about seafloor spreading. Finally, we’ll travel around western North America to see the features created by the different types of plate boundaries there.

Chapter Outline

Chapter Summary


In the early 20th century, Alfred Wegener was the first persistent scientist to propose the idea that continents move around on Earth’s surface. The meteorologist amassed a tremendous amount of evidence but could not think of a mechanism that others would accept to explain how solid continents could plow through ocean basins. Wegener’s idea was abandoned. His continental drift idea was resurrected after World War II when scientists started to put together data about the seafloor. The astonishing features of the seafloor, the strange pattern of rock ages across the seafloor, and the history of the magnetic north pole on land, gave scientists in the early 1960s a great deal to mull over. From this work Harold Hess propose seafloor spreading as a mechanism for drifting continents. The resulting theory of plate tectonics is the explanation of what happens as plates of Earth’s lithosphere interact at different types of plate boundaries.

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Difficulty Level:
At Grade
Date Created:
Jul 23, 2013
Last Modified:
Jan 14, 2016
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