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Plate Tectonics

Plate Tectonics. Drifting Continents Chapter 17.1. Vocabulary . Continental Drift – the continents were joined as a single landmass that broke apart 200 mya Still drifting Pangaea – ancient landmass made up of all the continents

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Plate Tectonics

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  1. Plate Tectonics Drifting Continents Chapter 17.1

  2. Vocabulary • Continental Drift – the continents were joined as a single landmass that broke apart 200 mya • Still drifting • Pangaea – ancient landmass made up of all the continents • Alfred Wegener – found evidence to support the theory of continental drift

  3. Evidence of the Drift • Rock formations • Large geologic structures, such as mountain ranges fractured as the continents split • There should be similar rock types on opposite sides of the Atlantic • Rocks on the Appalachians are identical to rocks in Greenland and Europe

  4. Evidence of the Drift • Fossil formations • Similar fossils of several different animals and plants that lived on or near land had been found on several different continents • Land dwelling animals could not possibly have swum the great distances between continents • Trilobites • Ages of fossils predated the breakup of Pangaea

  5. Evidence of the Drift • Climatic evidence • Fossils of plants indicating the same type of climate have been found • On different continents • In current climates where they wouldn’t have survived

  6. Evidence of the Drift • Coal deposits • In Antarctica show that the land must have been at one time closer to the equator • Glacial deposits • 290 million year old deposits found in warm climates • Land must have at one time been located near the south pole

  7. Evidence of the Drift • Wegener’s idea was generally rejected • Most scientists believed in the early 1900’s that the continents were fixed • 2 flaws in the theory • What force was strong enough to move the continents? • How could the continents move through solids?

  8. Plate Tectonics Seafloor Spreading 17.2

  9. Vocabulary • Sonar – use of sound waves to detect and measure objects under water

  10. Magnetic reversal – when Earth’s magnetic field changes polarity between normal and reversed Magnetic field demo

  11. Magnetometer – used to map the ocean floor by detecting small changes in magnetic fields

  12. Sometimes the magnetic field of the earth completely flips. • The north and the south poles swap places. • Such reversals, recorded in the magnetism of ancient rocks, are unpredictable. • They come at irregular intervals averaging about 300,000 years; • the last one was 780,000 years ago. Are we overdue for another? No one knows.

  13. Isochron – imaginary line on a map that shows points of the same age; formed at the same time • Seafloor spreading – ocean crust is formed at mid-ocean ridges and destroyed at deep-sea trenches • Continuous cycle of magma intrusion and spreading

  14. Ridges and Trenches

  15. Mid-Atlantic Range – chain of underwater mountains that run throughout the ocean basins • Lenth of 65,000 km • Contains active and extinct volcanoes

  16. Topography – change in elevation in the crust

  17. Tectonic Plates Plate Boundaries 17-3

  18. Tectonic plates • Huge pieces of crust and upper mantle that fit together at their edges to cover Earth’s surface • 12 major plates and several minor plates • Move slowly • In different directions and at different speeds in relation to each other • Edges are called boundaries

  19. Types of Boundaries • Divergent (divide) Boundary • Convergent (collision) Boundary • Transform Boundary

  20. Divergent Boundaries • Definition – place where two of Earth’s tectonic plates are moving apart • Associated with volcanism, earthquakes, and heat flow • Found primarily in the seafloor

  21. Divergent Plate Boundaries

  22. Rift valley – long, narrow depression that forms when continental crust begins to separate at divergent boundaries

  23. Convergent Boundaries • Three types • Oceanic – Oceanic • Oceanic – Continental • Continental – Continental • Subduction – process by which one tectonic plate slips beneath another tectonic plate

  24. Oceanic – OceanicConvergent Boundary

  25. Oceanic – Continental Convergent Boundary

  26. Continental – ContinentalConvergent Boundary Subduction zone

  27. Transform Boundaries – most likely to cause earthquakes

  28. Transform Boundaries

  29. Convection Chapter 17.4

  30. Back to Wegener • Remember the two flaws to his theory of continental drift? • What type of force could possibly move the continents? • How do the continents move through solids?

  31. Convection is the answer!!! • Large scale motion in the mantle • Transfer of thermal energy by the movement of heated material

  32. Let’s talk about States of Matter • As matter cools • It contracts • Becomes denser • Cooled matter than drops due to gravity • Warmer matter • Is displaced • And then rise

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