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Introduction to Plate Tectonics Plate Tectonics The theory of plate tectonics best explains the evolution of the earth’s landforms. A German scientist named Alfred Wegener first proposed the Theory of Continental Drift in 1912. 200 million years ago all the continents were grouped together in one large land mass called Pangea. The earth’s crust is divided into 20 plates. The plates move because they are resting on the partially melted rocks of the asthenosphere. Slowly flowing convection currents move the plates in various directions. Three Basic Boundaries Converging Plate Boundaries Two plates moving toward each other The collision can cause the lithosphere to be pushed up into a mountain range. Example: The Himalayas formed from India pushing northward into China. Subduction Plate Boundaries A type of converging plate boundary where one plate is plunged downward under the overriding plate. When an oceanic plate collides with a continental plate, the lighter ocean plate is subducted underneath the continental plate. Forms a mountain chain and a deepsea trench. Deep & strong earthquakes. Main Convergent Boundaries The Ring of Fire is a volcano & earthquake zone that encircles the Pacific Ocean. EQ Magnitude less than 5.0 Earthquake and Volcano Data EQ Magnitude 5.0 to 6.9 EQ Magnitude 7.0 and above Volcano Diverging Plate Boundaries: Two plates are moving away from each other The Mid-Atlantic Ridge is the spreading center, which separates the North American Plate from the Eurasian Plate and the South American Plate from the Africa Plate. The MAR was formed by the solidification of magma as the older rock moves aside. Main Divergent Boundaries Transform Plate Boundaries Two plates are sliding past one another – causes earthquakes Example: San Andreas Fault has resulted from the North American Plate sliding past the Pacific Plate.