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CH 9 PLATE TECTONICS Roots: Derm = skin (dermatitis) Diplo = two (diploid) Dis – away (disappear) Dia = through (diagonal) Dict = speak (dictate) Domin = master (dominate) Don = give (donation) Duct = lead (conduct) Du = two (duplicate) Dur = lasting (durable) Past or Future? Future Plates: http://earth.rice.edu/MTPE/geo/geosphere/topics/plate_tectonics/plate_future.mov
“Alfred! ALFRED! ALFRED WEGENER!” Do you think when Alfred’s mom called him in for dinner she had even the slightest idea what a monumental effect her son would have on the world as we understand it? Alfred grew up to develop the hypothesis of CONTINENTAL DRIFT. He proposed that there had been a supercontinent in Earth’s past and he named it PANGAEA.
Evidence for Continental Drift: The Continental Puzzle! Evidence: The continents fit together like a mega-puzzle. Bullard Fit of Continents: http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm ACTIVITY: Making Pangaea puzzles.
Breaking up is so hard to do! “It’s not you … it’s me.“ “Let’s just be friends.” “We need to talk…” “You’re like a brother to me.” “Give me my ring.” Pangaea breakup (slow-mo) http://www.agci.org/classroom/geosphere/index.php Continental Drift as Linked to Paleologic Time Scale http://www.wiley.com/college/strahler/0471480533/animations/ch13_animations/animation3.html
Evidence for Continental Drift: Continuous Mountains! Mountain Ranges: Ranges of mountains that stretch across multiple continents that once were attached. These mountains have the same rocks and composition. Grenville Orogeny
Evidence for Continental Drift: Continuous Climates!
? Wegener is rejected! Wegener couldn’t explain the mechanism (what was the force) that allowed the plates to move. A few scientists continued to search for answers.
Evidence for Continental Drift: Paleomagnetism! Magnetic iron-rich rocks heat up. Lose their magnetism. Cool down. Become re-magnetic in a direction parallel to the existing magnetic field around earth. Magnetic Reversals: http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm
Pg 266 Figure 17 Normal polarity = when rocks show the same magnetism as the current magnetic field. Reverse polarity = when rocks show opposite magnetism to the current magnetic field.
Evidence for Continental Drift: Earthquake Patterns! Relationship between deep focus earthquakes and ocean trenches. Weak Rock Pg 267 Figure 18 Earthquakes are produced during subduction where rocks are weak. Shallow-focus quakes are produced in the weak rock as the descending plate sinks. As the descending plate (and weak rock section) goes deeper the earthquake foci become deeper. No earthquakes have been produced below 700 km. This is where the rock begins to soften and melt.
Evidence for Continental Drift: Ocean Drilling! The Deep Sea Drilling Project 1968-1983 The Glomar Challenger drilled into the ocean floor. Older Oldest Young Youngest rocks are closest to the ridge.
Evidence for Continental Drift: Hot Spots! The formation of hot spot islands in a chain that corresponds with the movement of the plate. Hawaii Formation of Hawaiian Island Chain http://www.teachersdomain.org/resource/ess05.sci.ess.earthsys.hawaii/rm By 1968, a new theory was developed – Plate Tectonics.
Divergent = separating Convergent = coming together Transform = sliding past each other Animated Plate Boundaries (shows divergent, convergent, and transform) http://www.seed.slb.com/subcontent.aspx?id=5046
Seafloor Spreading = the process by which plate tectonics produces new oceanic lithosphere. • Pg 259 Figure 9 • Upwarping occurs • Rift valley is created • Linear sea developes • Oceanic ridge builds • Continents drift apart • Averages 5 cm/yr • All of Earth’s oceans could have been created within the last 200 million years. (Oldest found is 180 my) Sea Floor Spreading & Formation of Oceanic Crust: http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm HSW: Earth Science: The Spreading Seafloor Time: 04:01
Iberia Iceland Divergent Boundaries = where plates move away from each other iceland Basic Plate Boundaries: http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm
Continental Rifts = areas where spreading develops within a continent. East African Rift Valley The Process of Rifting: http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm
Convergent Boundaries = where plates come together Ocean – Continent Subduction Zone: Where an ocean plate is forced below a continental plate. Continental Volcanic Arc = where volcanic mountains are created due to subduction. Andes Basic Plate Boundaries & the Process of Subduction: http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm
Convergent Boundaries: Ocean – Ocean: Where two ocean plates collide. Aleutian Islands Island Arc Formation: http://esminfo.prenhall.com/science/geoanimations/animations/35_VolcanicAct.html
Continent – Continent Where two continental plates collide. Himalayas Continental plates are buoyant so neither wants to subduct below the other. As a result they simply collide and push up mountains. Formation of Himalayas: http://www.classzone.com/books/earth_science/terc/content/visualizations/es1105/es1105page01.cfm?chapter_no=visualization
Transform Boundaries = where plates slide past each other Basic Plate Boundaries & Transform Faults: http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm
Why do the Tectonic Plates Move? Convection in a pot of water. Main Reason: Convection. Convection around a heater. Convection at the sea shore.
Why do the Tectonic Plates Move? Slab-Pull = downward movement of convectional flow. Ridge-Push = sliding down of sides of ridge and pushing outward from the ridge. Flash: Continents Adrift