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Plate Tectonics

Plate Tectonics. Rearranging Earth’s Surface. Tectonic Processes. GOAL: To understand the processes behind the distribution of Earth’s continents and oceans. Tectonic Processes. Alfred Wegener and how a scientific paradigm operates Structure of Earth allows continents to move

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Plate Tectonics

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  1. Plate Tectonics Rearranging Earth’s Surface

  2. Tectonic Processes GOAL: To understand the processes behind the distribution of Earth’s continents and oceans

  3. Tectonic Processes • Alfred Wegener and how a scientific paradigm operates • Structure of Earth allows continents to move • Types of Plate Interactions • Divergence • Convergence • Transform 4. Hot Spots

  4. 1. Alfred Wegener and how a scientific paradigm operates "Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence. . . It is only by combing the information furnished by all the earth sciences that we can hope to determine 'truth' here, that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw." Alfred Wegener. The Origins of Continents and Oceans (4th edition)

  5. Field work: Atlantic once closed

  6. Shape MatchRocks MatchFossils MatchLifetime of work

  7. Theory of Continental Drift Meteorologist proposes to change geology 1st edition 1915

  8. Earlier, Sir Francis Bacon Wondered about similar shape of South America and Africa coastline

  9. Until 1960s – Utter Rejection by Geologists Dr. Rollin T. Chamberlin of the University of Chicago said, "Wegener's hypothesis in general is of the footloose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories." American Association of Petroleum Geologists organized a symposium specifically in opposition to the continental drift hypothesis. "Utter, damned rot!" W.B. Scott, President of the American Philosophical Society

  10. Today: We Map Tectonic Plates

  11. Classroom Resources Folder Today: We Accept that most Earthquakes and Volcanoes occur along boundaries of Tectonic Plates

  12. Today: We Accept Plate Movement

  13. Today: We Accept Pangaeaand its breakup

  14. Pangaea Breakup Resources Earth in the Future Animation of Drift Over Time

  15. Online Video Presentations

  16. Why the opposition & shift? • An example of how a discipline can get “locked into” a pathway of mental thinking for decades (paradigm), rejecting the idea of moving continents. • An example of how a discipline protects its “turf” – rejecting the thoughts of a meteorologist. • Enough time for the opponents to die, and a bunch of new geologists in the 1960s to challenge “the establishment”. • Reminder throughout this class that ideas shift and much depends on the mental framework of the scientist

  17. 2. Structure of Earth allows continents to move Wegener could not answer a fundamental question of HOW continents could move. But geology advanced to the point to begin to understand Earth’s internal structure & how it allows continental drift

  18. Structure and Internal Energy   • Knowledge of Earth’s Interior is incomplete – we’ve only explored about 1/1000 of Earth’s radius • Inferential knowledge through monitoring of shockwaves transmitted through Earth from earthquakes or human-made explosions • Four main zones of the Earth’s Interior • Earth’s Core: Deepest part of the Earth • Inner Core: supposedly solid, dense (iron/nickel or iron/silicate • Outer Core: (molten) liquid shell beneath the mantle that encloses the inner core

  19. Structure and Internal Energy (cont.) • Earth in Cross Section 3. Earth’s Mantle: Surrounds the outer core, largest of all four shells; believe 3 zones within mantle • Lithosphere: uppermost zone of mantle & crust together • Asthenosphere: “plastic” layer; below lithosphere • Mesosphere: rigid part of mantle; below asthenosphere 4. Earth’s Crust: outermost layer; mixed rock types • Mohorovičić discontinuity (Moho): boundary between earth’s crust & mantle

  20. Earth in Cross Section

  21. Earth’s Interior

  22. Earth’s Interior

  23. Core to Crust

  24. Earth’s Structure

  25. Brittle Crust Floats on Flowing Asthenosphere

  26. Different Crusts: 5/6th submerged(isostatic balance) Ocean Crust Continental Crust Dense (sima) Lighter (sial)

  27. ISOSTACYCrust adjusts to create a balance (equilibrium)

  28. Human Induced Change

  29. 2 continental plates under Tibet To reach isostatic balance, Tibet Plateau rises Too thick, so get uplift

  30. Effects Of Erosion on Isostacy

  31. Earth oozes at different rates Asthenosphere flows Even the crust adjusts

  32. Reason for Movement Excess heat from radioactive decay creates liquid outer core (and magnetic field), and forces mantle to have convection

  33. Exactly how mantle moves? ASU view

  34. Classroom Resources Animation of a theoretical model showing sinking crust and rising hot plumes – all in the mantle

  35. Stream Systems on Dynamic Earth 3. TYPES OF PLATE INTERACTION

  36. 3. Type of Plate Interactionsa. Divergent Boundaries • Mid-ocean • ridges are • places of • plate divergence

  37. Mid-Atlantic Ridge is the Icon

  38. Mid • Atlantic • Ridge • East • Pacific • Rise • Mid Indian • Ridge

  39. Why a ridge? Why not a Valley? Heat makes the large structure rise up, but at the axis there is a rift valley from spreading

  40. Sea Floor Spreading: Key to Rejecting the Old Ways “Plate Tectonics” = continental drift + sea-floor spreading Rename the theory with new evidence: • Potassium-Argon dating • Paleomagnetism

  41. Potassium - Argon Dating Discovery: middle of ocean ridges youngest

  42. Millions of years before present

  43. Classroom Resources Animation showing ages of ocean crust getting older away from spreading

  44. Paleomagnetism

  45. Classroom Resources Visualizing reversals of magnetic field and how this creates a mirror image on the two sides of a spreading center

  46. Lava has minerals that “record” the magnetic field

  47. Paleomagnetism in Symmetry Conclusion was that Sea floors Spreading apart

  48. Source for Latest Info: Website

  49. Continents can also spread Africa is Rifting Atlantic Opened up

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