Continental Drift • Some continents look like they fit like puzzle pieces • Ex. South America and Africa • Alfred Wegner proposed theory of continental drift. • Continental drift, continents have moved slowly to their current locations.
Pangaea • Wegener proposed, 200 million years ago, the continents were one landmass. • He called the landmass Pangaea. • Pangaea meaning “all land”
Wegener’s theory was highly controversial, due to his lack of proof. • He proposed that continents plowed through the ocean floor because of the spin of the earth. • It wasn’t until the 1930’s and after his death that his hypothesis was accepted, due to advancements in technology.
Fossil Clues • Fossil gave support to Wegner’s idea. • Fossils of the reptile Mesosaurus have been found in South America and Africa. • Another fossil that supports the hypothesis of continental drift is Glossopteris. found in Africa, Australia, India, South America, and Antarctica.
Climate Clues • Fossils of warm-weather plants were found on the island of Spitsbergen in the Arctic Ocean. • Wegner hypothesized it drifted from a tropical region.
Rock Clues • Similar rock structures found on different continents. • Appalachian Mountains similar to those found in Greenland and Western Europe.
Wegner, could not explain, when, why, or how. • Move to How the Earth was made film
Seafloor Spreading • Sound waves used to measure depth of ocean floor • Method used during World War II, and rifts, valley, and mountains were found. • Looked similar to continents
In rift valleys, volcanic eruptions and earthquakes discovered. • Ridges called mid-ocean ridges • Harry Hess came up w/ Seafloor Spreading Theory.
Hot, less dense material rises toward the surface at the mid-ocean ridges. • Then flows sideways, carrying the seafloor away from the ridge in both directions. • This creates new seafloor. • New seafloor closer to ridge • Older seafloor moves away from ridge
Magnetic Clues • http://www.youtube.com/watch?v=GyMLlLxbfa4&feature=related • Magnetic poles will reverse themselves. South becomes North and North becomes South. • Rock samples along the ridge demonstrate this change in polarity over time.
Parallel line of rock, demonstrates normal and reverse polarity on each side of the ridge. • http://www.youtube.com/watch?v=BCzCmldiaWQ
__________ is the hypothesis that continents have slowly moved to their current locations. • A. Continental drift • B. Mid-ocean shifting • C. Pangaea • D. Seafloor spreading
Who proposed the hypothesis of continental drift? • A. Esker • B. Gagarin • C. Hess • D. Wegener
What is Pangea? • Pangaea means “all land” and is the name that Wegener used to refer to the one large landmass that he believed existed before it broke apart into continents.
What is seafloor spreading? • Seafloor spreading is the process in which hot, less dense material below Earth’s crust rises toward the surface at the mid-ocean ridges. This material flows sideways and carries the seafloor away from the ridge in both directions.
How did scientists realize that the ocean floor was not flat, and what did they discover? • During WWII, the military used sonar to look for submarines. What they found were different depths, which when compiled, showed, canyons and mountains like that on earth.