1. Plate Tectonics 8 th Grade Science

2. Earth’s Composition

4. Tectonic Plates - Pieces of lithosphere that move around on asthenosphere -Earth’s lithosphere is broken into about 19 pieces -Fit like pieces of a giant jigsaw puzzle -Some plates contain only continental crust, some have only oceanic crust, some have both

5. Map of Tectonic Plates

6. Tectonic Plate Close-Up

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

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

9. 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.

10. Fossil Evidence

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

12. 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.

13. Sea-Floor Spreading

14. 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.

15. Magnetic Reversal

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

17. 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

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

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

24. 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.

25. Convection

26. 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…..

27. Pangaea Ultima