Theory of Continental Drift Continental Drift Alfred Wegener 1912 Theory that all landmasses were once joined: Pangaea Evidence of Continental Drift Coastlines Coasts of Africa and South America (among others) match like puzzle pieces Mountain Chains Ancient mountain chains match up across continents Coal Fields Fields in Brazil match those in Africa Glacial Deposits Deposits of material from glaciers match in Africa, India, South America, Australia and Antarctica Glacial Deposits Found in tropical climates Glacial Striations Grooves carved by glaciers match up in various continents Climate changes Deposits not fitting climate Salt- too far from equator Coral- non-tropical areas Coal in cold, dry areas Fossil Evidence Fossils of organisms out of climates survive in Glossopteris Plant- seed dispersal;arctic area Lystrosaurus Reptile in arctic regions Weakness of Theory Wegener could not explain how continents moves Acceptance of Theory Occurred when understood Earth’s structure Core Mantle Asthenosphere Crust/Lithosphere Earth’s tectonic plates Movement of Plates Interior of Earth hot-radioactivity Creates convection currents Crust “floats” on asthenosphere of mantle Convection Currents Movement of Plates Isostacy Balance between upward force of mantle and downward force of crust Earth’s Crust and Isostacy Oceanic crust more dense Float lower on mantle Continental crust less dense Float higher on mantle Continental and Oceanic Crust Erosion carries sediments to oceans Oceans not fill up-float lower Less material on crust- float higher on mantle Crust always balanced on the mantle .