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Continental Drift. Chapter 10 Section 1. Continental Puzzle. Do the continents fit together perfectly? What continents fit the best? What other information would you look for to provide evidence that continents may have once been part of one large continent?.
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Continental Drift Chapter 10 Section 1
Continental Puzzle • Do the continents fit together perfectly? • What continents fit the best? • What other information would you look for to provide evidence that continents may have once been part of one large continent?
Alfred Wegener & Continental Drift • 1912 proposed supercontinent • Pangaea • Continents separated and drifted apart
Evidence • Coastline similarities • Fossils • Rock formations • Climates
Coastline Similarities • Continents on either side of Atlantic ocean seem to fit together • Contours of eastern coast of South America fit along the contours of the western coast of Africa
Fossils • Mesosaurus – reptile fossils found only in southern South America and western Africa • Glossopteris – plant fossils found in South America, southern Africa, India, Australia, and Antarctica (Southern Hemisphere)
Rock Formations • Mountain ranges of eastern South America (Brazilian Highlands) and western Africa (Cape Mountains) are the same • Mountain ranges in north eastern North America (Appalachian Mts.), Greenland, Scotland and northern Europe (Caledonian Mts.) are the same
Climates • Glacial evidence in South America, Antarctica, India, Australia and Africa • When viewed separately, glacial evidence on these continents suggests that the entire earth was covered with glaciers at one time, but this is contradicted by other evidence from sedimentary rocks • When continents are placed together, like a puzzle, glacial evidence is not world-wide, which coincides with other evidence • Tropical plant fossils in Antarctica • No plants currently grow in Antarctica, so plant fossils found there indicate warmer temperatures at one time
Alfred Wegener and Continental Drift • Despite the evidence that seemed to suggest Pangaea, Wegener’s continental drift hypothesis was rejected by the scientific community • If the continents were moving apart, why wasn’t the Earth expanding? • Continents don’t plow through oceanic rock, so how can they move? • There was no evidence for the mechanism of tectonic plates or their movement
Evidence for the Theory of Plate Tectonics • In the mid part of the 20th Century, discoveries were made as a result of Naval technologies that enables the mapping of the sea floor • Hitler had gotten very close to the U.S. in WWII, via submarines (in the coastal waters of the eastern seaboard) • U.S. raced to learn more about the ocean floor in order to develop better submarine capabilities
Mid-Ocean Ridges and Rift Valleys • 1947 mapping project • sonic technology enabled the mapping of the sea floor • Rift valleys and mid-ocean ridges were discovered • Rift valley – a rip, or rift, in a tectonic plate at which volcanic activity is found • Mid-ocean ridge – the mountain ranges found on either side of a rift valley, formed from magma building up on either side of a rift
Paleomagnetism • Magnetometers developed during WWII to detect submarine hulls also discovered that Earth’s rock record contains magnetic reversals • Normal magnetism and reverse magnetism alternates in rocks during specific periods • Magnetic symmetry – magnetic bands (reverse and normal) are mirror images on either side of mid-ocean ridges • Suggests that magnetism of Earth changes • Metals in molten magma align with the magnetism at the time of crystallization • Igneous rocks (basalt) retain the magnetic orientation at time of formation
Additional observations of Ocean Floors • Ages of ocean floor features increase in age as distance from the ridge increases • Sediments are thinner and younger nearer ridge • Fossils are younger nearer ridge • Rocks are younger nearer ridge • All this suggests that new oceanic crust is forming at the rift valleys
Tectonic Plate Boundaries http://www.bing.com/videos/search?q=volcanoes+and+earth+quakes&FORM=HDRSC3#view=detail&mid=0F70E0C062BAAA8F5BCE0F70E0C062BAAA8F5BCE
“Ring of Fire” • Area of high seismic and volcanic activity outlining the Pacific Ocean
Conservation of Energy • According to the law of conservation of energy, energy can’t be created nor destroyed. • What is the source of energy that drives volcanoes? • What energy source produces earthquakes?
Lithosphere • Crust and upper portion of mantle
Lithosphere • Broken into blocks called tectonic plates • Each plate may include continental crust, oceanic crust, or both • Continental crust thicker and less dense than oceanic crust
Lithosphere • About 15 major tectonic plates
Lithosphere • Tectonic plates “float” on Asthenosphere – solid, putty-like (“plastic”) rock below lithosphere • Asthenosphere flows very slowly
Tectonic Plates Interact • The tectonic plates of Earth’s lithosphere form the pieces of a very tightly-fitting puzzle. • Since plates move over the asthenosphere, they are bound to interact with each other • Plates interact at their boundaries in 3 major ways
Types of tectonic plate boundaries • Divergent Plate Boundaries • Convergent Plate Boundaries • Transform Plate Boundaries
Divergent Plate Boundaries • http://www.youtube.com/watch?v=2q4Yqctq6nE
Divergent Plate Boundaries Boundary between tectonic plates that are diverging (moving apart) • Common features • Mid-ocean ridges • Rift valleys • Seafloor spreading • Volcanic activity • Seismic activity
Examples • Mid-Atlantic Ridge • Red Sea – separation of African and Arabian plates
Transform plate boundary • Boundary between plates that slide past each other • Common features • Earthquakes • Faults • Example: San Andreas Fault • Offset surface features
Convergent plate boundary • Boundary between tectonic plates that are converging • Three types of collisions • Oceanic-continental collision • Oceanic-oceanic collisions • Continental–continental collisions
