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Plate Tectonics

Plate Tectonics. KWL then Birth of a theory. The Earth’s surface is made up of moving , solid pieces called plates (Reference Tables). Some of these plates are moving together and some are moving apart . Plate tectonics is the study of the formation and movement of these plates.

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Plate Tectonics

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  1. Plate Tectonics KWL then Birth of a theory

  2. The Earth’s surface is made up of moving, solid pieces called plates (Reference Tables). Some of these plates are moving together and some are moving apart. Plate tectonics is the study of the formation and movement of these plates.

  3. The Earth’s plates are part of the lithosphere. The lithosphere considered to be the crust and the upper part of the mantle. The oceanic crust is mainly made of the igneous rock basalt, while the continental crust is made of the igneous rock granite. Oceanic crust is denser than continental crust.

  4. The lower part of the mantle is called the asthenosphere. This layer has similar composition to the upper mantle, but it is partially melted. This makes the asthenosphere like a very thick “liquid”

  5. The “liquid” property of the asthenosphere allows it to flow very slowly. • You can think of the lithospheric plates as “floating” on the asthenosphere.

  6. The heat from inside the Earth causes convection currents to form in the asthenosphere. • Where the convection currents rise, new material (molten rock) forces the plates apart. • Where the convection currents are sinking, the plates are moving together.

  7. ConvectionCells

  8. Convection currents: drag and move the lithospheric plates above the asthenosphere (three sources of heat produce the convection currents): Leftover heat from earth’s formation Decay of Radioactive elements Plate friction So, what causes plates to move?

  9. Convection Currents in the mantle drag and pull the lithospheric plates above them

  10. ARROWS IN THE ASTHENOSPHERE SHOW PLATE MOVEMENT DUE TO CONVECTION

  11. The arrows shown in the asthenosphere represent the inferred slow circulation of the plastic mantle by a process called (1) insolation (3) conduction (2) convection (4) radiation

  12. II. Evidence of Plate Movement: Continental Drift

  13. http://www.classzone.com/books/earth_science/terc/content/visualizations/es0806/es0806page01.cfm?chapter_no=visualizationhttp://www.classzone.com/books/earth_science/terc/content/visualizations/es0806/es0806page01.cfm?chapter_no=visualization The shape of the west coast of Africa and the east coast of South America seem to fit together like a puzzle. It is believed that they were once together, but moved apart over time (Continental Drift).

  14. Evidence for plate tectonics and continental drift Pieces fit together like a jig-saw puzzle. Particularly South America and Africa

  15. Wegener used documented cases of fossil organisms (land animals) that had been found on different continents that could not have crossed the current oceans.

  16. 2. Similar fossil remains in Africa and South America of a reptile that is found nowhere else in the world.

  17. Matching Mountain Ranges 3. Distinctive rocks were also found in Africa and South America in regions where the two continents were most likely joined together.

  18. 4. The majority of earthquakes and volcanoes are found in belts that occur along plate boundaries (where the plates are moving). Ex. the Pacific Ring of Fire.

  19. A new hope:Sea-Floor Spreading MID-ATLANTIC RIDGE 50,000 km. Long mountain range on the ocean floor

  20. BrainPop- Plate Tectonics

  21. Evidence for Plate Tectonics • During WWII, the U.S. in an effort to find any advantage that would help out submarines in the war effort, scientists found that the iron in the rock at the mid-ocean ridge sometimes pointed North and sometimes pointed South

  22. How could this be? • Basalt is iron rich and contains magnetite. Magnetite acts like a little magnet and aligns itself with the orientation of earth’s magnetic field. • When magma solidifies, the alignment is “locked in” recording Earth’s magnetic orientation at the time of cooling.

  23. MAGNETIC STRIPE EVIDENCE North Oriented Rocks are said to have NORMAL POLARITY South Oriented Rocks are said to have REVERSED POLARITY

  24. The earth’s magnetic field has reversed hundreds of times http://www.classzone.com/books/earth_science/terc/content/visualizations/es0803/es0803page01.cfm?chapter_no=visualization

  25. POLARITY FLIPPING AGE INCREASES AWAY FROM OPENING - RIDGE

  26. Older Older Youngest

  27. 5. Magnetic polarity reversals are recorded in rocks on the ocean floor as the sea floor spreads apart. During certain periods in Earth’s history, the magnetic fields have reversed (a compass would point south during a reversal). Minerals containing iron found in the igneous rocks on the ocean floor would shift before the magma cooled and hardened.

  28. If the polarity changed, the new magma would cool with the minerals shifted in the opposite direction. This change is recorded in the rocks.

  29. Which graph best represents the geologic age of the surface bedrock on the ocean bottom?

  30. 6. Heat flowing out of the rocks is greatest where the rocks are spreading apart (rising convection current), and decrease as you move away from the center (sinking convection currents). HOT! HOT! HOT!

  31. Glacier Evidence Not in notes Woohoo Animations!!!!! http://highered.mcgraw-hill.com/sites/0072402466/student_view0/chapter19/animations_and_movies.html#

  32. Plate Tectonics An Introduction WS

  33. “Uh-Oh!”: Problems with Continental Drift….

  34. …an alternate explanation? 1928: Arthur Holmes suggested magma rises toward the crust, spread, and sinks again. (Convection current) 1930: Wegner dies, unable to adapt Holmes’ idea to his theory.

  35. Mantle/Crust Structure

  36. Evidence for Plate Tectonics  Ocean Drilling • The data on the ages of seafloor sediment confirmed what the seafloor spreading hypothesis predicted. • The youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.

  37. Standard Deviants – Plate Tectonics

  38. Sea-Floor Spreading is aDivergent Plate Boundary Creates New Crust

  39. III. Kinds of Plate Boundaries • Diverging Boundaries- this is where the plates are moving apart at spreading centers (on the ocean floor). These boundaries form mid-ocean ridges or rises (like underwater mountain ranges). Between the peaks of the ridge are valleys called rift valleys. Ex. mid-Atlantic Ridge

  40. SPLITS APART CONTINENTS TO CREATE NEW OCEANS

  41. Spreading Center

  42. New Ocean forming – linear Red Sea When it grows up, it will be like the Atlantic Ocean

  43. EAST AFRICAN RIFT VALLEY – CONTINENTAL RIFT

  44. In Afar, Ethiopia, a 40-mile magmatic rift that opened up 1 year ago

  45. As the name implies, this is where two plates are sliding past each other. The sliding movement often causes earthquakes to occur. This happens along faults. A fault is nothing more than a crack in the Earth’s crust where movement has occurred. B. Sliding Boundaries!!! Ex. North American Plate and the Pacific Plate are sliding past each other along the San Andreas Fault in California

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