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Continental Drift Plate Tectonics

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  • 1. Continental Drift & Plate Tectonics
  • 2. Continental Drift Theory
    • First proposed by Alfred Wegener in 1912:
      • 250 million years ago, all of the continents were combined into one super-continent called “Pangaea”
      • The continents gradually drifted apart to where they are today
    • Wegner didn’t make up this theory out of the blue – like all scientists, he based it on evidence
  • 3. Evidence Summary
    • Geographic fit of South America and Africa
    • Fossils match across oceans
    • Rock types and structures match across oceans
    • Ancient glacial features
  • 4. Geographic Fit
    • Continents look like they could be part of a giant jigsaw puzzle
    • Here’s how they moved apart
  • 5. Fossils Match
    • Plant and animal fossils found on the coastlines of different continents
  • 6. Fossil Fuel in Antarctica
    • Tropical plant remains (coal deposits) found in Antarctica
      • this is evidence that Antarctica was once much warmer and much closer to the equator, since tropical plants don’t grow in Antarctica today
  • 7. Rock Structures Match Across Oceans
    • Same rock patterns found in South America, India, Africa, Antarctica and Australia
  • 8. Rock Structures Match Across Oceans
  • 9. Ancient Glacial Features
    • Glaciation in Africa, South America, India, and Australia during the same time
  • 10. Ancient Glacial Features
  • 11. Evidence but no Method
    • While Wegener presented compelling evidence, there was still no explanation for HOW the continents drifted.
    • The question remained: “If continents drift, what is making them move?”
  • 12. Sea Floor Discoveries
    • WW II: Military Spending
    • U.S. Navy mapped seafloor with sonar in order to help ships and submarines navigate.
    • They expected to find that the ocean floor was a vast, flat plain. What they found was shocking.
  • 13. Sea Floor Discoveries
    • Instead of miles and miles of flat surface, they found that the ocean floor had:
      • oceanic ridges - submerged mountain ranges
      • fracture zones - cracks perpendicular to ridge
      • trenches - narrow, deep gashes
      • seamounts - drowned undersea islands
  • 14. Sea Floor Discoveries
    • In addition, they discovered that the rocks of the seafloor included only basalt, gabbro, and serpentinite - no continental materials .
    • This suggested that the sea floor was not simply “covered up” continental crust, but was made of different materials and at a different time
  • 15. Sea Floor Discoveries
    • Further study of these rocks led scientists to even more surprising information:
    • The sea floor’s youngest rocks were located right at the ocean ridge – and as you moved away from the ridge in either direction, the rocks got progressively older.
  • 16. Sea Floor Discoveries
  • 17. Sea Floor Discoveries
    • What scientists discovered was that the sea floor was being constantly “recycled.” The youngest rocks were created from magma rising to the surface, hardening and pushing aside the older rock.
    • Scientists called this process “sea floor spreading.”
  • 18. Sea Floor Discoveries
    • So now we know:
      • sea floor is being created at the mid-ocean ridges
      • sea floor is spreading
      • the oldest ocean floor occurs at the coastlines of continents…
    • Why doesn’t the earth get bigger? Where does the ocean floor go? Why doesn’t it get any older?
  • 19. Sea Floor Discoveries
    • The ocean floor is pushed against the continental crust – and because it is denser, it dives under the crust.
    • This process is called subduction
  • 20. Sea Floor Discoveries http://www.youtube.com/watch?v=Zl89Owshdjo
  • 21. The Rise of Plate Tectonics
    • In the late 1950’s, the United States was engaged in The Cold War with the Soviets
    • To keep an eye on Soviet nuclear tests, the U.S. military developed new, advanced seismometers
    • These seismometers were deployed in over 40 allied countries and were recording 24 hrs/day, 365 days/year
  • 22. The Rise of Plate Tectonics
    • Besides nuclear tests, the seismometers recorded every moderate to large earthquake on the planet.
    • Scientists mapped the earthquake data and found something they weren’t expecting:
      • Armed with this high-precision earthquake data, seismologists found that activity happens in narrow bands.
  • 23. The Rise of Plate Tectonics
  • 24. The Rise of Plate Tectonics
    • The discovery of these bands led scientists to understand that the earth’s outer shell is broken into thin, curved plates that move laterally atop a weaker underlying layer.
    • Think of it like a hard-boiled egg: you can put cracks all over the shell of a hard-boiled egg, but the egg is still “whole”
  • 25. Types of Plate Boundaries
    • The interaction of the plate edges with each other can be classified as one of three main types of boundaries:
    • Convergent boundaries
    • Divergent boundaries
    • Transform boundaries
  • 26. Types of Plate Boundaries
    • Convergent: areas of plates that are moving toward each other
      • there are three sub-types of convergent boundaries:
        • oceanic to continental
        • continental to continental
        • oceanic to oceanic
  • 27. Types of Plate Boundaries
    • Divergent: areas of plates that are moving away from each other
  • 28. Types of Plate Boundaries
    • Transform: areas of plates that are sliding past each other
  • 29. Types of Plate Boundaries
    • Here’s an animation of each type of plate boundary
  • 30. Types of Plate Boundaries
  • 31. Types of Plate Boundaries http://www.youtube.com/watch?v=ho21AyKgD00
  • 32. Review the Facts Continental Drift Sea Floor Plate Tectonics 1 pt 2 pt 3 pt 1 pt 2 pt 3 pt 1 pt 2 pt 3 pt Go To Exit Slip
  • 33. Continental Drift 1 pt
    • The scientist who first proposed the theory of continental drift
  • 34. Continental Drift 1 pt Answer
    • Who was Alfred Wegner?
  • 35. Continental Drift 2 pt
    • fossils match across continents and oceans, same rock patterns found on five different continents, mountain ranges match across the Atlantic ocean
  • 36. Continental Drift 2 pt Answer
    • What is some of the evidence Wegner used to support his theory that the continents were once joined?
  • 37. Continental Drift 3 pt
    • Because he had no answer to the question, “If the continents are drifting, what mechanism is causing them to move?”
  • 38. Continental Drift 3 pt Answer
    • Why was Wegner’s theory of continental drift widely ignored?
  • 39. Sea Floor 1 pt
    • ocean ridges, fracture zones, trenches, seamounts
  • 40. Sea Floor 1 pt Answer
    • What did Harry Hess and the US Navy discover when they mapped the sea floor using sonar?
  • 41. Sea Floor 2 pt
    • The process of ocean crust “diving” under other crust into the mantle
  • 42. Sea Floor 2 pt Answer
    • What is subduction?
  • 43. Sea Floor 3 pt
    • The process by which the newest ocean floor is created at mid-ocean ridges, pushing older crust outward
  • 44. Sea Floor 3 pt Answer
    • What is sea floor spreading?
  • 45. Plate Tectonics 1 pt
    • What the earth’s outer shell is broken into
  • 46. Plate Tectonics 1 pt Answer
    • What are plates?
  • 47. Plate Tectonics 2 pt
    • Instrument deployed by US Military to spy on soviet nuclear tests which also detected medium-to-large earthquakes.
  • 48. Plate Tectonics 2 pt Answer
    • What is a seismometer?
  • 49. Plate Tectonics 3 pt
    • The three ways plate boundaries interact
  • 50. Plate Tectonics 3 pt Answer
    • What are convergent, divergent, & transform?
  • 51. Review – Exit Slip
    • Choose what you believe to be the strongest piece of evidence Wegner uncovered to support the idea of continental drift and explain why you think it is the most convincing.
    • If new sea floor is constantly being created, why isn’t the earth growing in size?
    • How did earthquakes help scientists to understand the structure of the earth’s crust?
  • 52.
    • © Jan Parker, 2010 – for purchaser’s classroom use only; please do not distribute. If other teachers in your school like what they see, send them to my website http://www.thesciencevault.com or to my web store http://www.teacherspayteachers.com/Store/Jan-Parker 
    • If you put your classroom materials on a server for your students, please post this presentation in pdf form. Thanks!