1. Plate Tectonics

2. The Theory of Seafloor Spreading 1.On the ocean floor there are areas where the seafloor is getting bigger. 2.Researchers used sound waves to discover a system of underwater ridges or mountains that can be found all over the world.

3. The scientist

4. Mid Ocean Ridges This underwater chain of mountains and volcanoes. –Most known ones are Mid Atlantic Ridge and East Pacific Rise AKA oceanic spreading centers http://www.youtube.com/watch?v=DWKWdfJtNl 0 http://www.youtube.com/watch?v=6CsTT mvX6mchttp://www.youtube.com/watch?v=6CsTT mvX6mc

5. Why does the Seafloor Spread? 1.Hot, Less dense material below Earth’s crust rises upward to the surfaces at the mid ocean ridges. 2.Then, it, flows sideways, carrying the seafloor away from the ridge. 3.As the seafloor spreads apart, magma moves up and flows from the cracks, cools, and forms new seafloor.

7. Cross section view Oldest youngest

9. 2 Types Slow moving Fast moving

10. Slow Moving Mid Atlantic Ridge About an (1) inch a year Really wide gap between each side “cooler “

11. Fast moving “hotter” (there is a constant presence of hot asthenosphere) East pacific rise Like taffy being pulled Growth is varied

13. Evidence for Seafloor Spreading Youngest rocks are located at mid-ocean ridges. Oldest is near the continent

14. Oldest youngest

15. Evidence

16. Evidence for Seafloor Spreading 1.Reversal of Earth’s magnetic field are recorded by rocks in strips parallel to ridges. 2.These iron rich rocks point towards magnetic North wherever it is at the time they cool.

17. Paper activity

18. Normal Reverse

19. Reverse polarity Normal polarity

21. Discussion Question How could seafloor spreading be related to continental drift?

22. Answer If the Seafloor is constantly spreading apart and moving, it will effect and move the continents as well.

23. Theory of Plate Tectonics Earth’s crust and upper mantle are broken into sections called plates, they move on a plastic-like layer of the mantle. Crust and rigid upper mantle form the lithosphere. Plastic-like layer below is called asthenosphere.

24. Plate Boundaries Divergent Plate boundaries –Plates moving apart.

25. Convergent Boundaries –Plates moving together. –Denser plates sink under less dense plates. –Newly formed hot magma forced upward forms volcanic mountains

26. Plates collide Plates crumple up to form mountain ranges. Earthquakes are common

27. Transform boundary –Plates slide past one another. –Sudden movement can cause earthquakes

28. Convection inside the Earth is thought to be the force behind plate tectonics. Features caused by plate tectonics –Faults and rift valleys –Mountains and volcanoes –Strike- slip faults – cause of earthquakes.