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Plate Tectonics

Plate Tectonics. What do you notice about the continents when you look at a map of the Earth?. Continental Drift. Hypothesis that all continents were once connected in a single large landmass that broke apart Alfred Wegener (1912) Pangaea (all land) – name of large landmass

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Plate Tectonics

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  1. Plate Tectonics

  2. What do you notice about the continents when you look at a map of the Earth?

  3. Continental Drift • Hypothesis that all continents were once connected in a single large landmass that broke apart • Alfred Wegener (1912) • Pangaea (all land) – name of large landmass • Not accepted until 1930 (after his death) • Later evidence used to support hypothesis

  4. Evidence for Continental Drift • Shape of Continents • Fossil Clues • Mesosaurus (fresh water / land reptile) • Glossopteris (fern) • Climate Clues • Warm weather fossils in cold areas • Glacial deposits in warm areas • Rock Clues • Similar rock structures on different continents • Similar mountain ranges

  5. Seafloor Spreading

  6. Mapping the Ocean Floor • Early ideas about seafloor - flat • Early on -line lowered to the floor • Sonar – • Sound waves “bounced” off seafloor • The longer it takes to arrive back at ship, the deeper the seafloor is • Maps made from this sonar information • Mountains and trenches discovered

  7. Seafloor Spreading • Theory developed in 1960’s • Harry Hess (Princeton) • Hot, less dense material below crust rises at mid-ocean ridges • Flows sideways, carrying the seafloor with it away from the ridge in both directions • Magma forced up, it cools and forms new seafloor • Seafloor moving away from ridge cools, contracts, and becomes more dense and sinks back down to be melted

  8. Evidence for Seafloor Spreading • Age of rocks – newest rock at mid-ocean ridges, older rock the farther away from the ridge you go • Magnetic clues • Iron-bearing minerals line up with the magnetic pole • Switch in magnetic pole = switch in the way the minerals line up • Magnetometer – instrument used to detect magnetic fields

  9. Theory of Plate Tectonics

  10. Plate Tectonics • Combined continental drift and sea-floor spreading theories • 1960’s • Earth’s crust and part of the upper mantle are broken into sections (plates) that move over the mantle. • Lithosphere – less dense, rigid layer (about 100 km thick) • Asthenosphere – more dense, plastic-like layer below the lithosphere

  11. Types of Plate Boundaries • Divergent – • Boundary formed when plates move apart • Ridge or Rift formed • Convergent – • Boundary formed when plates collide • 2 Continental plates = mountains • Continental plate + ocean plate = trench and volcanoes • Transform – • Boundary formed when plates slide past one another • Can move in opposite directions or in the same direction at different speeds • Earthquakes

  12. Divergent Plate Boundaries

  13. Convergent Plate Boundaries

  14. Transform Plate Boundaries

  15. Cause of Plate Tectonics • Convection Currents • Hot magma in mantle rises (less dense) • Magma reaches crust and moves sideways • Magma cools and sinks back down into mantle (more dense)

  16. Convection Currents

  17. Earthquakes

  18. Causes of Earthquakes • Earthquake – the vibrations produced when rocks break • Fault Formation • Rocks act like bending sticks rather than rubber bands • Bend until elastic limit is reached = break • Fault – surface along which rocks move when they pass their elastic limit and break

  19. Types of Faults USGS ANIMATIONS

  20. Normal Fault (tension)

  21. Reverse Fault (Compression)

  22. Reverse Fault

  23. Reverse Fault

  24. Reverse Fault (Compression)

  25. Strike-slip Fault

  26. Earthquake Animation

  27. Features of Earthquakes • Seismic Waves – energy wave generated by an earthquake • Focus – the point below the earth’s surface where energy is released • Epicenter – point on the earth’s surface directly above the earthquake focus

  28. Types of Seismic Waves • Primary (P) waves – • Cause rock particles to move back & forth in the same direction • Travel through any material • 6 km / sec. • Secondary (S) waves – • Cause rock particles to move at right angles to the direction of movement • Travel only through solids • 3.5 km / sec • Surface waves – • Cause most of the destruction • Waves that reach Earth’s surface and travel outward from the epicenter in all directions

  29. Locating an Epicenter • Seismograph – instrument used to record seismic waves • Seismic stations • The larger the distance time between P- and S- waves, the farther from the epicenter the station is • 3 stations are needed to pinpoint the epicenter

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