Theories: CONTINENTAL DRIFT This theory stated that all the continents in the world were joined together a long time ago. The great big super continent (which he called Pangaea) cracked apart into several big pieces and slowly, over time drifted to their present locations. This theory supposed that Pangaea was whole 250 million years ago when the world was populated with dinosaurs and other extinct creatures Feb 3 10:12 AM Feb 3 7:48 AM A famous scientist, Alfred Wegener, proposed the theory of continental drift. He believed that by gathering data on 1. Landforms: (mountians, coal fields) 2. Fossils: (Mesosaurus, Lystrosaurus, Glossopteris) 3. Climate: (glacier deposits and sctatches, fossilized warm/cold "typical" plants and animals) 4. Fit of the continents: Continents look like they fit together Feb 3 8:27 AM Feb 3 8:33 AM Alfred Wegener Inuit guide Feb 3 8:36 AM Feb 3 8:40 AM 1
Feb 3 8:33 AM Feb 3 8:33 AM Fossil evidence Feb 3 8:38 AM Feb 3 8:36 AM Climate evidence Why Wegener was a reject... or... Why Wegener's theory was rejected and he died cold and alone on an ice shelf in Greenland... He couldn't explain HOW the continents got to their present location...that wasn't done for another 30 years Feb 3 8:39 AM Feb 3 8:33 AM 2
Proof that Wegener was right!!!!! This was a new theory... it was based in Wegener's original data of 1. Fit of continents 2. Fossils 3. Landforms 4. Climate BUT... Poor Alfred!... Tried to explain HOW the continents were capable of moving Feb 3 8:39 AM Feb 3 8:33 AM The Theory of Plate Tectonics Proposed in the 50's and 60's What is the theory? "...is a theory that describes the formation, movement, and interaction of... plates." The theory explains the geological processes that take place (largely on the ocean floor) to make the plates move There are 3 Primary pieces of evidence that support this theory... 1. Location of earthquakes and volcanoes 2. Age of the ocean floor 3. Magnetic polarity of ocean floor Feb 3 9:57 AM Feb 3 10:03 AM Feb 3 8:48 AM Feb 3 8:47 AM 3
Feb 3 8:47 AM Feb 3 8:50 AM Remember the layers of Earth??? Ahhhh...we love the layers of the earth! They're so dynamic and mysterious Mar 26 8:19 AM Feb 3 8:40 AM Well the thinnest layer, the crust, is somewhat more complex than you may originally think, considering it's so darn thin... Mar 26 8:20 AM Mar 26 8:21 AM 4
plate tectonics and continental drift.notebook Styrofoam VS. Metal Mar 26 8:02 AM Because of the density differences between the types of crust, it will have a HUGE effect on how it moves on the asthenosphere. Mar 26 8:24 AM Because continental crust is so buoyant, it will never get subducted, or pulled down into the mantle. It's like trying to keep a piece of Styrofoam submerged under water Mar 26 8:25 AM Mar 26 8:27 AM There are three (3) primary type of boundaries 1. Divergent: Two plate moving away from each other. *common features of diverging plate boundaries include mid ocean ridges (if diverging is taking place on the ocean floor rift valleys earthquake activity (usually found along the "fracture zones at mid ocean ridges volcanic activity (lava flows) Feb 4 8:02 AM Feb 3 8:46 AM 5
Convergent boundaries: Where two plates are moving toward each other. There are 3 types of convergent boundaries... 1. Oceanic/oceanic convergent (subduction)...remember when two plates move toward each other the denser plate will be subducted, in this case it will be the older, colder oceanic plate * common features of oceanic/oceanic subduction include.. 1. deep sea trenches 2. volcanic island arcs 3. earthquakes 2. Oceanic/continental convergent (subduction)...remember oceanic plates are ALWAYS more dense than continental plates so the oceanic plate will ALWAYS subduct * common features of oceanic/continental subduction include 1. deep sea trench 2. volcanoes along the coast of the continent 3. earthquake activity 3. Continent/continent (COLLISION)...remember continental plates are "light" and NEVER subduct so when they converge neither plate will be subducted. Instead they will collide together and get crumpled and folded into huge mountains * common features of continental/continental convergence include 1. high continental mountain chains 2. earthquake activity Feb 4 8:11 AM Feb 3 8:57 AM Feb 3 8:58 AM Feb 4 8:44 AM Transform boundary (two plates scraping horizontally past each other...also known as fracture zones along the mid ocean ridge * common features of transform boundaries 1. earthquake activity Feb 3 8:59 AM Feb 4 8:44 AM 6
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Mar 27 10:57 AM Mar 27 10:59 AM What causes the plates to move? * they're huge! * they're heavy! * what force is so strong that it is capable of moving these gigantic slabs of heavy rock?!!!!! Three (3) theories for forces that can cause plate movement 1. Mantle convection: convection currents in the mantle, heated from below by the core shunt the lithospheric plates around like rafts in an ocean Upwelling areas are associated with diverging boundaries Downwelling areas are associated with converging boundaries Feb 3 8:57 AM Feb 4 8:49 AM Ridge push: Occurs at mid ocean ridges Associated with diverging plates molten rock that rises from the asthenosphere at divergent boundaries wells up into the crack caused by diverging plates. the rock is quickly hardened, but much hotter than the surrounding rock, so it occupies a greater volume, causing it to be elevated above the sea floor. Colder rock farther away from the M.O.R is colder and therefore more dense (occupying less volume). This denser rock "pulls" on the younger rock pulling it away from the M.O.R. a.k.a gravitational sliding...thought to have the least force for moving the lithospheric plates Feb 3 9:05 AM Feb 4 9:16 AM 8
Slab pull occurs at subduction boundaries associated with converging (subduction) boundaries the process of subduction forces a cold, dense plate into the mantle. The subducting plate is denser than the surrounding material so continues to sink deep into the mantle as it melts... as this happens it pulls the rest of the plate down with it. (at the same rate new oceanic material is being created at the opposing diverging plate, so the lithospheric plate continues to be created and destroyed in an never ending cycle. very much like a conveyer belt in a grocery store Feb 4 9:24 AM Feb 4 9:07 AM So...if the plates are moving so slowly, how do we actually KNOW that they are moving at all?... good, old fashioned surveying Feb 3 9:08 AM Feb 3 9:02 AM satellite data Feb 3 9:02 AM Feb 3 9:06 AM 9
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