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Seafloor Spreading Hypothesis

Seafloor topography, magnetic polarity and age are evidence for seafloor spreading, the mechanism for continental movement.

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Putting Plates Together

Putting Plates Together

Credit: USGS
Source: http://en.wikipedia.org/wiki/File:Plates_tect2_en.svg
License: CC BY-NC 3.0

The theory of plate tectonics was put together during the first half of the 20th century. The work of many people contributed to the construction of this extremely important theory in Earth Science.

Amazing But True!

  • Alfred Wegener thought the continents had moved around Earth’s surface but he had no mechanism for how they could plow through the oceans.
  • Harry Hess solved Wegener’s problem when he discovered seafloor spreading, which was the mechanism for continental movements.
  • Plate tectonics theory explains how earthquakes happen along plate boundaries, how volcanoes form above subduction zones, and many other geological observations.
  • Credit: Jose F. Vigil. USGS
    Source: http://en.wikipedia.org/wiki/File:Tectonic_plate_boundaries.png
    License: CC BY-NC 3.0

    Cross section showing different types of plate boundaries [Figure2]

Show What You Know

With the links below, learn more about plate tectonics. Then answer the following questions.

  1. What was the first evidence that Alfred Wegener had that the continents had all once been part of a single landmass?
  2. What did Harry Hess discover about the ages of rocks in the Atlantic Ocean?
  3. Why did Harry Hess think that oceanic crust should be recycled? Where does this recycling take place?
  4. Why do volcanoes erupt above subducting plates?
  5. What happens when plates lock?

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Image Attributions

  1. [1]^ Credit: USGS; Source: http://en.wikipedia.org/wiki/File:Plates_tect2_en.svg; License: CC BY-NC 3.0
  2. [2]^ Credit: Jose F. Vigil. USGS; Source: http://en.wikipedia.org/wiki/File:Tectonic_plate_boundaries.png; License: CC BY-NC 3.0

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