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Continental Drift and Plate Tectonics Principles of Science Mr. Porter Earth’s 3 Main Layers 1. Core - made of solid iron and nickel 3,500 km thick. Core Outer Core Earth’s 3 Main Layers 2. Mantle – Mostly solid rock, but the top is partly melted. 2,800 km thick. Mantle Earth’s 3 Main Layers 3. Crust - Top layer of the Earth. Very thin, only 8 to 70 km thick. Continents and ocean floor are part of the crust. Crust Continental Drift Continental drift - A theory that states all the continents used to be joined in 1 giant continent called Pangea, then they drifted apart. 1912- the German scientist, Alfred Wegener proposed this theory to explain why Africa and South America could fit together. Continental Drift (Additional Evidence) 1. Similar fossils were found on different continents. Continental Drift (Additional Evidence) 2. Mountain ranges and rock layers seemed to continue from continent to continent. • Rock types in Brazil match those in West Africa. • Appalachian Mtns have limestone similar to Scotland’s Highlands Continental Drift (Additional Evidence) 3. Glacial deposits found near equator. • South African rock formations show evidence of ice sheet scratches Seafloor Spreading • Mid-oceanic ridge - long, underwater mountain range • discovered by scientists after WW II. • Rift valley – A deep valley that splits the ridge in half. • Magma is continually coming up from within the valley creating new sea floor crust and pushing the old sea floor apart. Seafloor Spreading Plate Tectonics Plate tectonics states that the Earth’s crust is made up of large sections, or plates, that are in motion. Plates move in 3 different ways Plate Tectonics Plate Tectonics 1. Convergent - Collide with Each other. Plate Tectonics 2. Divergent - Move Apart. Plate Tectonics 3. Transform Slide Past Each Other. Plate Tectonics The pushing, pulling, and grinding of plates cause earthquake and volcanoes. Scientists believe convection currents allow for plate movement. Convection Current - circular movement of a liquid or gas as it heats. Plate Tectonics Review Q’s 1) Which layer of the Earth do we stand on? 2) Which layer of the Earth is the thickest? Thinnest? 3) List 3 pieces of evidence that support continental drift. 4) What is Pangea? 5) How does the theory of plate tectonics explain how the continents were moved thousands of miles from each other? Homework Continental Drift Foldable Take a separate sheet of paper and do a horizontal fold (hamburger fold). Then take the edges and fold them back to the spine. Design and color the foldable to show how the theory of continental drift works.