Continental Drift Hypothesis proposed by Alfred Wegener in 1915 The idea that Earth’s continents were once joined in a single landmass and gradually drifted apart. This was not believed until the mid-1900’s Wegener found many things that he claimed proved his hypothesis

Evidence for Continental Drift Fossils Ancient reptile found in both South America and Western Africa - Mesosaurus Evidence for Continental Drift

Geology Rocks in Brazil matched perfectly to rocks in Africa Limestone in Appalachian Mts. (N.A.) same as Scottish Highlands

Evidence for Continental Drift Climate The same glacial till of the same age is found in southern Africa, South America, India and Australia Large coal deposits were formed from tropical swamps in both N. America and Europe at the same time

Super Continent Wegener named his super continent Pangaea From the Greek word meaning “all lands” Was a continent that reached from pole to pole Began to split apart 200 million years ago

New Evidence In the 1960’s scientists really started studying the sea floor Found underwater mountain ranges Called mid-ocean ridges Found in every ocean Seemed to circle the Earth like the seams of a baseball Sea-floor Spreading Where the ridges form Cracks in the crust where molten rock rises, cools, and forms new crust

New Evidence Age of the Sea Floor Rock near the cracks are younger then rocks further away Ocean Trenches Where the oceanic crust sinks back into the Asthenosphere Scientists put this new evidence together with Wegener's hypotheses to create the Theory of Plate Tectonics

Theory of Plate Tectonics States that Earth’s lithosphere is broken into huge plates that move over the surface of the Earth Driving force of this movement is the convection current in the Asthenosphere Most major earthquakes, volcanoes, and mountain ranges are where two plates meet.

What causes Plate Movement Convection Current Motion that transfers heat energy in a material As molten rock heats up it becomes less dense, as it rises it starts to cool becoming more dense and sinking again

Convection Currents Create Ridge Push Happens at mid-ocean ridges Pushes plates apart Creates new sea floor Slab Pull Happens at Ocean Trenches The denser plate sinks Melts back into the Asthenosphere

Hot Spots Area where hot molten rock rises to the surface in plumes (columns) from the mantle Usually found in the middle of tectonic plates but can be near boundaries Hawaiian Islands Can tell the direction and speed of plate movement Yellowstone National Park Sometimes found at divergent boundaries Iceland Azores Galapagos Islands

Magnetic Reversal Recorded in the sea floor Magnetic minerals in igneous rock lines up according to the direction of the poles Last one was about 760,000 yrs ago Flipped 170 times over the last 100 million years The prediction for it happening again is 1,500 – 2,000 yrs from now