"San Francisco 1906-

            
             "The Greatest earthquake on United States History-.
             -First of all I want to explain what a "plate tectonics- is.
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             Plate tectonics are a relatively new theory that has revolutionized the way geologists thinks about the Earth. According to the theory, the surface of the Earth is broken into large plates. The size and position of these plates change over time. The edges of these plates, where they move against each other, are sites of intense geologic activity, such as earthquakes, volcanoes, and mountain building. Plate tectonics is a combination of two earlier ideas, Continental Drift and Sea-floor Spreading. Continental drift is the movement of continents over the Earth's surface and in their change in position relative to each other. (Pherson 270).
             A German meteorologist Alfred Wegener originally developed the Continental drift concept in 1912. Some of the key facts that he used to support his theory are the shape and fit of the continents and the distribution of similar fossils and rock layers around the planet. Based on his observations Wegener proposed that all of today's modern continents were once part of a "Super Continent-, which is today known as Pangea.
             This is the possible process that the Earth went thru over the past 550 millions of years:.
             550 millions 220 millions .
             of years ago. of years ago.
             190 millions 136 millions .
             of years ago of years ago. .