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Theory of Continental Drift vs. Plate Tectonics Essential Question: Explain the Theory of Continental Drift and the Plate Tectonics Theory. Looking at the world map, what do you notice about the shape of the continents? The thing is…the world didn’t always look like this! It used to look like this: This super land mass was connected into one piece called Pangaea Theory of Continental Drift •Alfred Wegner – in 1910 noticed that the continents fit like puzzle pieces, thought that at one time they were all together as one huge continent •Pangaea – meaning “all land”, the super continent that existed about 200-300 million years ago •Theory of Continental Drift – Wegner’s idea that continents slowly moved (this idea was not excepted by others at the time) Theory of Continental Drift •Evidence – • plant and animal fossils that were identical even though they were found on opposite sides of the Atlantic Ocean. • Mountain ranges and layers of rock on both sides of the Atlantic Ocean Matched. • Glacial Movement, fossils of plants and animals embedded in rocks in the Arctic that were known to be tropical. Seafloor Spreading • In the early 1960’s Harry Hess proposed seafloor spreading. • He believed that molten rock rises from the mantle along mid ocean ridges, forcing the crust to move in opposite directions and creating a new seafloor in the process. • He also believed that crust was being destroyed as it sinks into deep ocean trenches in a process called subduction. • Based upon these two discoveries Alfred Wegner’s ideas were finally accepted. Convection Currents • Arthur Holmes – in 1929 suggested that the Earth’s Mantle had convection currents that were strong enough to carry the continents around. • Convection Currents: • the transfer of heat by the circulation or movement of the heated parts of a liquid or gas. Ocean currents, air currents, mantle currents Plate Tectonics Theory •Earth’s surface is fractured just like the shell of a cracked egg. •These fractures outline large plate-like chucks of the Earth’s crust. •These plates are floating on the mantle, drifting apart 1-10 cm yearly, sometimes colliding into other plates. •Earthquakes and volcanoes occur on the edges. •Mountain ranges form where continents collide. Difference between the two Theories… •Plate tectonic theory states that the entire crust moves, not just the continents.