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Tectonic Plates Pangea- A super continent that held all our modern continents. QuickTime™ and a GIF decompressor are needed to see this picture. This super continent broke apart and formed modern continents. Similar fossils have been found on Different continents. Remains of warm-weather plants in _______________ areas and glacial deposits in__________________ areas suggest that continents have moved. At first, continental drift was not accepted because no one could explain ____________ or __________continents had moved. Alfred Wegener proposed the hypothesis of continental drift in 1911 Wegener's Idea Using ______________ waves, scientists discovered a system of underwater mountain ranges called the mid-ocean ridges in many oceans. Ocean Ridges Courtesy of www.ngdc.noaa.gov In the 1960s, Harry Hess suggested the theory of ______ __________ to explain the ridges. QuickTime™ and a GIF decompressor are needed to see this picture. Hot, less dense material below Earth’s ______________ rises upward to the surface at the mid-ocean ridges. Then, it flows sideways, carrying the _______________ away from the ridge. As the seafloor spreads apart, ______________ moves up and flows from the cracks, cools, and forms new seafloor. Evidence for seafloor spreading _________________ rocks are located at mid-ocean ridges. Youngest at ridge Progressively older away from ridge Courtesy of www.ngdc.noaa.gov Mirror image across the ridge Reversals of Earth’s _________________ field are recorded by rocks in strips parallel to ridges. Plate movements 1.Earth’s ______________ and upper mantle are broken into sections. 2.The sections, called _______________, move on a plasticlike layer of the mantle. 3.The plates and upper mantle form the ____________________. 4.The plasticlike layer below the lithosphere is called the ______________________. Plate movements Plates moving ______________—divergent boundaries Iceland Iceland has a divergent plate boundary running through its middle Plates moving _________________ —convergent boundaries a.Denser plates sink under less ______________ plates. b.Newly formed hot ______________ forced upward forms volcanic mountains. Plates collide a.Plates crumple up to form _________________ ranges. b.____________________ are common. Plates slide past—called __________________ boundaries; sudden movement can cause earthquakes Convection inside Earth—the cycle of heating, rising, cooling, and sinking of material insideEarth is thought to be the ______________ behind plate tectonics. Features caused by plate tectonics 1.Faults and _____________ valleys 2.Mountains and ___________________ 3.Strike-slip faults—cause of ____________________ Testing for plate tectonics—scientists can measure __________________ as little as 1 cm per year.