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Continental Drift Plate Tectonics
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Continental Drift Plate Tectonics

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  • 1. Continental Drift & Plate TectonicsContinental Drift & Plate Tectonics
  • 2. Continental Drift TheoryContinental 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 SummaryEvidence Summary • Geographic fit of South America and Africa • Fossils match across oceans • Rock types and structures match across oceans • Ancient glacial features
  • 4. Geographic FitGeographic Fit • Continents look like they could be part of a giant jigsaw puzzle • Here’s how they moved apart
  • 5. Fossils MatchFossils Match • Plant and animal fossils found on the coastlines of different continents
  • 6. Fossil Fuel in AntarcticaFossil 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 OceansRock Structures Match Across Oceans • Same rock patterns found in South America, India, Africa, Antarctica and Australia
  • 8. Rock Structures Match Across OceansRock Structures Match Across Oceans
  • 9. Ancient Glacial FeaturesAncient Glacial Features • Glaciation in Africa, South America, India, and Australia during the same time
  • 10. Ancient Glacial FeaturesAncient Glacial Features
  • 11. Evidence but no MethodEvidence 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 DiscoveriesSea 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 DiscoveriesSea 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 DiscoveriesSea 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 DiscoveriesSea 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 DiscoveriesSea Floor Discoveries
  • 17. Sea Floor DiscoveriesSea 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 DiscoveriesSea 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 DiscoveriesSea 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 DiscoveriesSea Floor Discoveries http://www.youtube.com/watch?v=Zl89Owshdjo
  • 21. The Rise of Plate TectonicsThe 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 TectonicsThe 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 TectonicsThe Rise of Plate Tectonics
  • 24. The Rise of Plate TectonicsThe 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 BoundariesTypes 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 BoundariesTypes 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 BoundariesTypes of Plate Boundaries • Divergent: areas of plates that are moving away from each other
  • 28. Types of Plate BoundariesTypes of Plate Boundaries • Transform: areas of plates that are sliding past each other
  • 29. Types of Plate BoundariesTypes of Plate Boundaries • Here’s an animation of each type of plate boundary
  • 30. Types of Plate BoundariesTypes of Plate Boundaries
  • 31. Types of Plate BoundariesTypes of Plate Boundaries http://www.youtube.com/watch?v=ho21AyKgD00
  • 32. Review the FactsReview the Facts Continental Drift Sea Floor Plate Tectonics 1 pt1 pt 2 pt2 pt 3 pt3 pt 1 pt1 pt 2 pt2 pt 3 pt3 pt 1 pt1 pt 2 pt2 pt 3 pt3 pt Go To Exit Slip
  • 33. Continental Drift 1 ptContinental Drift 1 pt • The scientist who first proposed the theory of continental drift
  • 34. Continental Drift 1 pt AnswerContinental Drift 1 pt Answer • Who was Alfred Wegner?
  • 35. Continental Drift 2 ptContinental 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 AnswerContinental 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 ptContinental 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 AnswerContinental Drift 3 pt Answer • Why was Wegner’s theory of continental drift widely ignored?
  • 39. Sea Floor 1 ptSea Floor 1 pt • ocean ridges, fracture zones, trenches, seamounts
  • 40. Sea Floor 1 pt AnswerSea 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 ptSea Floor 2 pt • The process of ocean crust “diving” under other crust into the mantle
  • 42. Sea Floor 2 pt AnswerSea Floor 2 pt Answer • What is subduction?
  • 43. Sea Floor 3 ptSea 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 AnswerSea Floor 3 pt Answer • What is sea floor spreading?
  • 45. Plate Tectonics 1 ptPlate Tectonics 1 pt • What the earth’s outer shell is broken into
  • 46. Plate Tectonics 1 pt AnswerPlate Tectonics 1 pt Answer • What are plates?
  • 47. Plate Tectonics 2 ptPlate 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 AnswerPlate Tectonics 2 pt Answer • What is a seismometer?
  • 49. Plate Tectonics 3 ptPlate Tectonics 3 pt • The three ways plate boundaries interact
  • 50. Plate Tectonics 3 pt AnswerPlate Tectonics 3 pt Answer • What are convergent, divergent, & transform?
  • 51. Review – Exit SlipReview – 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. • THE FINE PRINT • © 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!

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