1. The Theory of Plate Tectonics 6 th Grade

2. Remember what we learned yesterday about continental drift? Alfred Wegener found a variety of evidence that suggested that the seven continents used to be joined together as one large supercontinent. What was the ONE PART of his theory that he was not able to explain?

3. Alfred Wegener was not able to explain the force that moved the continents

4. What force is great enough to move the heavy continents?

5. Geologists think that the movement of convection currents in the mantle is the major force that causes plate motion!

6. The Theory of Plate Tectonics: States that pieces of the Earth’s lithosphere called plates are in slow constant motion because of convection currents in the mantle

7. What are plates?

8. Plates: The lithosphere is broken into separate sections called plates Plates move around on top of the mantle like rafts

9. Plates fit together along cracks in the lithosphere

11. Review: What is the Lithosphere?

12. The solid upper part of the mantle = lithosphere –Less dense than the material below it so it “floats” on top of the asthenosphere

13. Review: What is the Asthenosphere?

14. Asthenosphere: semi-solid layer below the lithosphere ***The plates of the lithosphere float on the asthenosphere***

16. 2 Types of Plates Oceanic plates - plates below the oceans Continental plates - plates below the continents

17. Plate Boundaries

18. Remember that the convection currents (heat transfer) that are occurring in the mantle are causing these plates to move

19. Scientists use instruments on satellites to measure plate movement. Plates move at slow rates: ex. The North American and Eurasian plates are moving apart at 2.5 cm per year –about as fast as your fingernails grow

20. 3 types of tectonic plate movement : 1. Divergent 2. Convergent 3. Transform

21. Divergent Boundaries Boundary between two plates that are moving apart or rifting   RIFTING causes SEAFLOOR SPREADING

22. What is seafloor spreading? When oceanic plates diverge, (move apart) leaving room for molten material to erupt and cool This leads to the constant creation of new ocean floor This always occurs at the mid-ocean ridge

23. Seafloor Spreading at the Mid- Ocean Ridge

24. Mid-Ocean Ridge

26. Life at the Mid-Ocean Ridge

27. Features of Divergent Boundaries Mid-ocean ridges Rift Valleys

28. Rift Valley: when divergent boundaries occur on land

29. Great Rift Valley in Africa Volcanic mountains found along the rift include Mount Kilimanjaro, Mount Kenya and Mount Elgon extending from Jordan in southwestern Asia through eastern Africa to Mozambique 4,000 miles long, 30 miles wide

30. Great Rift Valley

31. Convergent Boundaries Boundaries between two plates that are colliding  

32. Oceanic plate colliding with a less dense Continental plate the dense oceanic crust sinks under the continental crust Causes TRENCHES

34. Oceanic plate colliding with another Oceanic plate The more dense plate slides under the less dense plate, creating a TRENCH

36. When 2 continental plates collide, both are about the same density Collision squeezes the crust into mountain ranges

38. Transform Fault Boundaries Boundary between two plates that are sliding past each other Creates “faults” or breaks in the Earth’s crust What do you think that this movement causes?

39. Earthquakes!

40. San Andreas Fault, CA

41. Questions... What are the three types of boundaries? What direction do plates go for each?

42. Understanding Plate Tectonics http://www.youtube.com/watch?v=tcPghqn nTVkhttp://www.youtube.com/watch?v=tcPghqn nTVk