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The Movement of the Continents Vocab Label as “Plate Tectonics and Continental Drift” on your vocab template. • • • • • • • • • • • • Contraction Theory Wegener Plate Tectonics and Continental Drift Pangaea Correlation Sea floor spreading Mid-ocean ridges Divergence Transformation Convergence Convection Currents Pangaea Ultima People Used to Believe… Contraction Theory- Continents were all connected like they are now, but massive cooling in the Earth collapsed land bridges between the continents. Plate Tectonics •proposed by Alfred Wegener in 1910. •noticed that the shorelines of the continents seemed • to ‘fit together’like the pieces of a giant jig saw puzzle. Wegener’s theory stated: 1) The continents were once all together in one place forming a supercontinent, Pangea. 2) The continents broke apart and drifted to their present locations. Wegener’s theory was not taken seriously because no one could believe that things as large as continents could move and because Wegener could not propose a mechanism which could explain such motion. -Continents and their tectonic plates Plate Movement and Land Changes Divergence (Separation)- When plates separate, they form sea floor spreading and ocean basins. Transformation- When plates slide past each other, they create fault lines that are prone to earthquakes. Convergence (when plates collide)- Mountains are pushed up/created. Today plate tectonics and continental drift are accepted as facts. Why? Let’s see the evidence! First, there’s Wegener’s original observation. The shorelines of the continents do fit together like the pieces of a puzzle. But that could just be a coincidence. For a theory to be accepted as fact, there must be more..................... Wegener’s Evidence • Fossils of the same animals, rocks, plants, etc were found to correlate (match up to eachother) in different parts of the globeparts that fit together like puzzle pieces. (Rainforest tree fossils found in the Arctic). (Ex: Mesosaurus) • Evidence of climates having at one time been the same in these puzzle piece areas. (Ex: The Karoo Desert in Africa shows marks that indicate the presence of Glaciers! Very cold in very hot?) • Resources not produced in certain biomes are mysteriously found there (Ex: coal found in the Artic when it is produced in Tropical Forests) Same fossils found on different continents These are the pictures on the puzzle pieces. Copyright © 2010 Ryan P. Murphy Example of fossil/rock similarities. Also findings that show similar past climates. Further Evidence •First, a series of under-water mountains called mid-ocean ridges are found throughout the world. •These mountains are formed as new sea floor is created from magma that wells up from the mantle below. As new sea floor is added it pushes the old sea floor Apart (Sea Floor Spreading) New sea floor is found at the mid ocean ridge where material is constantly being added. As distance from the ridge in either direction increases, so does the age of the rock. The Ultimate Proof 1992- the Laser Geodynamics/GPS Satellites (Lageos I and II) found that the continents are still drifting apart a few centimeters per year. . Let’s review the evidence for continental drift................................ 1) The continents seem to fit together like the pieces of a jig saw puzzle. 2) Same rocks from opposite shores. 3) Same fossils from opposite shores. 4) Sea floor spreading..... The existance of mid ocean ridges (mountain ranges) ..... 5) Direct satellite measurement of the drifting continents. Continental drift is now a well supported theory, but why is it happening??? How could continents, giant slabs of rock, possibly move? •Earth’s crust is a thin outer covering •Beneath the crust is the mantle. Hot rock in the mantle actually moves/flows slowly. •The deeper we go into the Earth, the hotter it gets. •Heat Rises and Cold Air sinks •This forms convection currents that rotate! •These convection currents in the mantle circulate and cause the continents above them to move. Continental Drift: The gradual movement of the continents across the earth. Copyright © 2010 Ryan P. Murphy • Wegener’s ideas were not accepted until the 1950’s!!! Copyright © 2010 Ryan P. Murphy • Same fossils found on different continents – These are the pictures on the puzzle pieces. Copyright © 2010 Ryan P. Murphy • Current Day In hundreds of millions of years, it is believed that the continents will create a “super continent” again by drifting together. This has been called Pangaea Ultima.