1. Plate Tectonics 8 th Grade Science

2. Earth’s Composition

3. Crust -Outermost layer – 5 to 100 km thick -2 types – Continental & Oceanic

4. Mantle -Much thicker layer – about 2,900 km -Contains most of Earth’s mass. -Molten rock -Magma comes from mantle

5. Core -Outer core – liquid iron & nickel -Inner core – solid iron & nickel

9. Tectonic Plates -Pieces of lithosphere that move around on asthenosphere -Fit like pieces of a giant jigsaw puzzle -Some plates contain only continental crust, some have only oceanic crust, some have both

10. Map of Tectonic Plates

11. Tectonic Plate Close-Up

12. Mapping Earth’s Interior -Seismic waves – earthquake waves -Travel through different densities & materials at different speeds

13. Alfred Wegener -Proposed Theory of Continental Drift -idea of once giant landmass (Pangaea) that broke & drifted to present locations.

14. Evidence for Pangaea -Continents seem to “fit” together. -Fossils of same plant & animal species found on opposite sides of oceans. -Same types of rocks & layers found on coasts on opposite sides of oceans. -Evidence of same climactic conditions on several continents.

15. Fossil Evidence

16. Pangaea & its Break Up -245 mya -existed while some of the earliest dinosaurs roamed. -Continents “broke” over time -Drifted to current locations

17. Sea-Floor Spreading -Tectonic plates move away from each other -New oceanic lithosphere forms as magma rises up & solidifies. -Older crust gets pushed further away. -Happens at Mid-Ocean Ridges.

18. Sea-Floor Spreading

19. Evidence for Sea-Floor Spreading -Records of magnetic reversal in ocean floor. -when Earth’s poles change, polarity of poles change. -Molten rock at ridges contain grains of magnetic material (iron) – act like little compasses. -Creates bands of grains pointing in opposite directions – bands are light/dark.

20. Magnetic Reversal

21. Plate Boundaries -Places where tectonic plates meet. -3 types: convergent, divergent, transform

22. Convergent Boundaries -2 plates collide or converge -3 types of convergent boundaries: 1. continental/continental – mountains form 2. continental/oceanic – subduction zones – volcanoes form 3. oceanic/oceanic – subduction – volcanoes -Subduction – sliding of one plate under another

25. Divergent Boundaries -2 plates separate or diverge -As they separate, magma rises to fill the gap -Forms mid-ocean ridges and rift valleys

27. Transform Boundaries -2 plates slide past each other horizontally -Plates grind & jerk as they slide -Produces earthquakes

29. Why do the Plates move? -CONVECTION CURRENTS in the MANTLE!!! -hot magma from deep inside Earth rises. -cools as it rises. -sinks back into deep Earth as it cools.

30. Convection

31. Pangaea Ultima? -Due to plate motion, the continents will continue to drift…… -One leading theory now is that they will all reunite into a giant landmass they call Pangaea Ultima. -Let’s take a look…..

32. Pangaea Ultima