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Plate Tectonics Rearranging Earth’s Surface. Tectonic Processes GOAL: To understand the processes behind the distribution of Earth’s continents and oceans.

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Presentation on theme: "Plate Tectonics Rearranging Earth’s Surface. Tectonic Processes GOAL: To understand the processes behind the distribution of Earth’s continents and oceans."— Presentation transcript:

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 1.Alfred Wegener and how a scientific paradigm operates 2.Structure of Earth allows continents to move 3.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 Match Rocks Match Fossils Match Lifetime of work

7 Theory of Continental Drift Meteorologist proposes to change geology 1 st 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." "Utter, damned rot!" W.B. Scott, President of the American Philosophical Society American Association of Petroleum Geologists organized a symposium specifically in opposition to the continental drift hypothesis.

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 Pangaea and its breakup

14 Resources Earth in the FutureAnimation of Drift Over Time Pangaea Breakup

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 1.Inner Core: supposedly solid, dense (iron/nickel or iron/silicate 2.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


22 Earth’s Interior


24 Core to Crust

25 Earth’s Structure

26 Brittle Crust Floats on Flowing Asthenosphere

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

28 ISOSTACY Crust adjusts to create a balance (equilibrium)

29 Human Induced Change

30 2 continental plates under Tibet To reach isostatic balance, Tibet Plateau rises Too thick, so get uplift

31 Effects Of Erosion on Isostacy

32 Earth oozes at different rates Asthenosphere flows Even the crust adjusts

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

34 Exactly how mantle moves? ASU view

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

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

37 3. Type of Plate Interactions a. Divergent Boundaries Mid-ocean ridges are places of plate divergence

38 Mid-Atlantic Ridge is the Icon

39 East Pacific Rise Mid Atlantic Ridge Mid Indian Ridge

40 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

41 Sea Floor Spreading: Key to Rejecting the Old Ways “Plate Tectonics” = continental drift + sea- floor spreading Rename the theory with new evidence: 1.Potassium-Argon dating 2.Paleomagnetism

42 Potassium - Argon Dating Discovery: middle of ocean ridges youngest

43 Millions of years before present

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

45 Paleomagnetism

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

47 Lava has minerals that “record” the magnetic field

48 Paleomagnetism in Symmetry Conclusion was that Sea floors Spreading apart

49 Source for Latest Info: Website

50 Continents can also spread Atlantic Opened up Africa is Rifting

51 Obvious question: with making new sea floor, why isn’t Earth expanding? Old ocean plates undergo “subduction”

52 3. Type of Plate Interactions b. Convergent Boundaries

53 Oceanic-Continental Convergence Denser Oceanic Crust Subducts Trench Forms Volcanoes Form Lithosphere Subducts Into Asthenosphere Earthquakes Common All Along Boundary

54 Andes Nazca plate collide with South American Plate Cartoon Recent Research from Nature

55 Classroom Resources Visualizations about the Andes Mtns as from Convergence of Ocean & Continental Plates

56 From the East-Pacific Rise, the Pacific plate moves towards subduction in the Aleutian Trench

57 Ocean-Cont. Convergence in Pacific Northwest

58 Island Arcs from Ocean-Ocean Convergence

59 Convergence of 2 continental plates Example of Himalaya

60 Classroom Resources Animations of Himalaya Formation

61 Formation of Appalachian Mountains resulted from the collision of the African and European Plates with North American Plate prior to 300 million years ago.

62 Ural Mountains Formation of the Ural Mountains related to collision tectonics prior to 300 Mya ago.

63 Convergence & Tsunami

64 Effects Of Plate Locking

65 EQ (or landslide or volcanic eruption) movement generates the wave that travels about 500 mph

66 Classroom Resources Shows how Tsunami can be made from subduction Shows time sequence in Tsunami destroying coastal city in Alaska

67 Animated gif

68 Mega-Quake Set off 2004 Tsunami & will happen again Energy ripple

69 Sri Lanka Sumatra Uplift

70 Indonesia


72 Has Happened, Will Happen Again Hilo, 1960 In Classroom Resources Folder, Animation of Chile EQ generating Tsunami that destroyed Hilo in 1960

73 3. Type of Plate Interactions c. Transform Boundaries Side-by-side motion along San Andreas zone

74 Transform motion of the San Andreas Fault can be seen by offset of streams that cross the fault zone.

75 California Won’t Fall into the Ocean Continent is 5/6ths submerged, so it is anchored very tight

76 Classroom Resource Animation showing how there used to be convergence along the California coast, but it turned into a transform boundary Animation of San Francisco Peninsula Topography shows the “gash” of the San Andreas fault zone

77 Other Transform Boundaries


79 4. Hot Spots Often in the middle of a plate Focus here on Hawaii

80 Hawaiian Hotspot





85 Classroom Resources Animation of Hawaii as moves over Hot Spot

86 Trail of the Hot Spot Note change in direction 43 myr ago Change in direction 43 myr ago

87 Alternative Hypothesis

88 Online Visualizations Tsunami Visualizations Plate Tectonic Movement Visualizations Isostacy Mountain Uplift ml Earth History me.html Mountain Building

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