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​ = = Plate tectonics Plate tectonics (from the Late Latin tectonicus, from the Greek: τεκτονικός "pertaining to building") is a theory which describes the large scale motions of Earth's lithosphere. The theory builds on the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegener, and seafloor spreading, developed in the 1960s.

**Continental Shift**  Alfred Wegener found that large-scale geological features on separated continents often matched very closely when the continents were brought together. Wegener also found that the fossils discovered in a certain place often indicated a climate utterly different from the climate of today: for example, fossils of tropical plants, such as ferns and cycads, were found on the Arctic island of Svalbad or Spitsbergen. All of these facts supported Wegener's theory which he called continental Drift In 1915 the first edition of The Origin of Continents and Oceans, a book outlining Wegener's theory, was published; expanded editions were published in 1920, 1922, and 1929. About 300 million years ago, claimed Wegener, the continents had formed a single mass, called Pangaea (from the Greek for "all the Earth"). Pangaea had rifted, or split, and its pieces had been moving away from each other ever since. Wegener was not the first to suggest that the continents had once been connected, but he was the first to present extensive evidence from several fields. Click on this to see a limited preview of the book, "The Original of Continents and Oceans" written by Alfered Wingener Plates can drift apart (sea floor spreading), push into each other or slide past each other.

=Sea Floor Spreading =

Seafloor spreading occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics. Picture Gallery

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