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Continental Drift Theory • Alfred Wegener • German meteorologist • 1912 Proposed single supercontinent Pangaea • Continental Drift Theory Continental Drift Theory 5 Types of Evidence • • • • • Fit of the Continents Distribution of Fossils Sequence of Rocks Glacier Scraping Patterns Ancient Climates and Wandering Polar Regions http://library.thinkquest.org/3669/media/map2dd.GIF Wegener’s Continental Drift Evidence: • Continents ‘fit’ together in a single land mass 250 mya • CLICK Simulations http://www.ucmp.berkel ey.edu/geology/anim1. html http://www.eoearth.org/upload/thumb/f/fb/Plate_tectonics_over_time.gif/400px-Plate_tectonics_over_time.gif Wegener’s Continental Drift Evidence : Plant and animal fossils of the same species were found on several different continents. Wegener’s Continental Drift Evidence: Similar sequence of rock or rock formations have the same age Wegener’s Continental Drift Evidence: Glacial deposits, striations, and scraping patterns Wegener’s Continental Drift Evidence: Climate distribution Past Present Coal exists under the ice in the rock of Antarctica – yet coal can only form from plants that grow in warm climates. Wegener’s Theory Problems 1) Wegener had no convincing mechanism (did not explain the forces) of how the continents might move. Continents plowing through the crust would destroy the crust. 2) Continents are not moving apart at the speed Wegener proposed. Wegener = 250cm/yr Actual = 2 cm/yr Holmes Breakthrough: Heat trapped in the Earth caused Convection Currents in the mantle. • As a substance is heated its density decreases and rises to the surface until it is cooled and sinks again. Convection currents • Gravity causes the heated mantle to sink • The mantle heats up near the core and then rises again • Conduction is the transfer of heat between 2 materials in direct contact with each other library.thinkquest.org/C003124/images/convect.jpg http://www.wisc-online.com/objects/index_tj.asp?objID=SCE304 Click animation New Evidence - Magnetic pattern of rock Volcanic rocks on the seafloor have magnetization because, as they cool, magnetic minerals within the rock align to the Earth’s magnetic field. North Magnetic Pole in No. Hemi North Magnetic Pole in So. Hemi Present Day North Magnetic Pole in No. Hemi Sea-Floor Spreading Hypothesis by Hess & Deitz CLICK Animation: http://www.uwsp.edu/geo/faculty/ritter/glossary/s_u/sea_flr_spread.html Plate Tectonics www.wiley.com/college/herenow/ptect/pt-map1.gif Plates ‘float’ on the Asthenosphere Plates have oceanic and continental crust Earth’s Layers • • • • • http://library.thinkquest.org/04oct/01724/images/Earth-crust-cutaway-english.png Inner Core Outer Core Mantle Crust Atmosphere • Lithosphere – crust and upper mantle, plates move independently • Asthenosphere-region below the Lithosphere Continental Crust http://www.amonline.net.au/geoscience/images/earth_diagrams/cont_oceanic_crust.gif • • • • • Cooling rate - slow Crystal size - large Density - less dense Thickest portion of the Earth’s outer layer Composition – made mainly of granite rock Oceanic Crust • • • • • Cooling rate - fast Crystal size - small Density – more dense Thinnest portion of the Earth’s outer layer Composition – Made mainly of basalt rock http://faculty.weber.edu/bdattilo/parks/plume_ocean.jpg Volcano- opening or rupture in the Earth’s crust that allows molten rock to escape http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes%20GCSE%20Bl og%20Resources/Images/Plate%20Tectonics/Plate%20Tectonics/VolcanoStructure.jpg Earthquake- result of sudden energy release in the Earth’s crust creating seismic waves. • http://news.bbc.co.uk/nol/shared/spl/hi/world/04/earthquake/img/earthquake.gif More Evidence- Location of mountain ridges, rift valleys, mid-ocean ridges, and trenches on plate boundaries. Convergent, Divergent and Transform http://www.ifa.hawaii.edu/~barnes/ast110_06/tprai/Tectonic_plate_boundaries.png SIMULATIONS ON ALL BOUNDARY TYPES CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/shockwave.html Andes Mountains Convergent Oceanic & Continental Plates move toward each other A trench is a steep walled valley on the sea floor. Subduction - A convergent boundary where one plate moves below the other plate blue.utb.edu/paullgj/images/Conv_Cont_Ocean.JPG CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/convergent.html Convergent Boundary Oceanic & Continental CLICK http://geology.com/nsta/convergent-boundary-oceanic-continental.gif Japan or Aleutian Islands Convergent Oceanic & Oceanic Denser oceanic crust subducts under less dense oceanic crust ceeps.colostate-pueblo.edu/.../smM1P1Fig15.gif Convergent Boundary Oceanic & Oceanic http://geology.com/nsta/convergent-boundary-oceanic-oceanic.gif Himalayas Convergent Continental & Continental: Faulting and Folding http://www.pbs.org/wgbh/aso/tryit/tectonics/crush.html Convergent Boundary Continental & Continental http://geology.com/nsta/convergent-boundary.gif Mid Atlantic Ridge Divergent Oceanic At a divergent boundary lithosphere plates move away from each other Divergent Boundary Oceanic • Mid-Ocean Ridges – a structure formed from seafloor spreading. CLICK http://geology.com/nsta/divergent-boundary-oceanic.gif East African Rift Valley Divergent Continental Rift Valley – Pulling apart of crust due to tensional forces ceeps.colostate-pueblo.edu/.../smM1P1Fig15.gif Divergent Boundary Continental • Rift Valley http://geology.com/nsta/divergent-boundary-continental.gif San Andreas Fault Transform Plate Boundary Plates slide past or laterally along each other www.wiley.com/college/herenow/ptect/pt-map1.gif Transform Boundary TRANSFORM SIMUALTIONS CLICK http://geology.com/nsta/transform-boundary.gif CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/transform.htm http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_plate_tectonics_world.gif Evidence - Location of earthquakes and volcanoes Hot Spot • Volcanoes that are found in the center of plates (not on plate boundaries) The Hawaiian-Emperor volcanic chain is the result of the drifting of the Pacific Plate over a fixed hot spot. http://geology.com/nsta/plate-tectonics-cover.gif The bend in the (Hawaiian – Emperor) volcanic chain is the result of a major change in the direction of the movement of the Pacific Plate. Location of Hot Spots Hot spots result from hot, narrow plumes of material that rise deep within the mantle. Plate Movement in the future • http://www.scotese.com/earth.htm It is even possible to measure the speed of continental plates extremely accurately, using satellite technology. External Energy For Earth • Sun & Moon keeps air and sea in motion, shapes surface • Sun warms atmosphere & crust unevenly creating winds • Winds drive ocean currents and water cycle • Erosion from winds, rains, rivers, glaciers, and waves shape surface • Weathering from winds and rains • Sun & Moon Gravitational Energy, produces tides • Planetesimal collisions Internal Energy for Earth • • • • • • Radioactive element decay Core heat from layers pressure Convection currents Volcanoes Hot Springs Earthquakes Evidence for Plate Tectonics First evidence used for Continental Drift Theory • Continents fit together • Fossil distribution • Glacier evidence: deposits, striations, scraping • Climate distribution • Common rock formations: same age New evidence • Magnetic pattern of rock • Location of earthquakes and volcanoes • Location of mountain ridges, rift valleys, mid-ocean ridges, and trenches Review: What is …? • • • • • • • • Hot Spot Rift Valley Trench Subduction Convection Current Sea Floor Spreading Mid Ocean Ridge Convergent, Divergent or Transform Boundary