2. Main Features of Plate Tectonics The Earth's surface is covered by a series of crustal plates.

3. Main Features of Plate Tectonics The ocean floors are continually, moving, spreading from the center, sinking at the edges, and being regenerated.

4. Main Features of Plate Tectonics Convection currents beneath the plates move the crustal plates in different directions.

5. Main Features of Plate Tectonics The source of heat driving the convection currents is radioactivity deep in the Earths mantle.

6. Plate Tectonics The tectonic plates are made up of the Earth’s crust and the upper part of the mantle layer underneath.

7. Plate Tectonics Lithosphere – top layer of the Earth made up of the crust and the top part of the mantle. Asthenosphere – solid but plasticlike layer on which the lithosphere sits. –Movement in this layer actually creates movement in the plates.

8. How Plates Move Heat from core causes magma to expand and rise Magma near the surface cools and condenses and falls This creates convection cells

9. How Plates Move Hot magma rises to the surface at spreading ridges and forms new crust. spreading ridges crust new crust pushes the rest of a plate out of its way.

10. How Plates Move Old parts of a plate sink down into the mantle at subduction zones because they are colder, thicker and denser than the warm mantle material underneath them. subduction zones

11. Question How is density used to explain plate movement?

12. Evidence for Plate Tectonic Theory Shapes of many continents look like they are separated pieces of a puzzle. For example –South America and Africa –North America and Europe

13. Evidence for Plate Tectonic Theory Many fossil comparisons along the edges of continents that look like they fit together. –This suggest species similarities that would only make sense if the two continents were joined at some point in the past.

14. Evidence for Plate Tectonic Theory

15. There is a large amount of seismic, volcanic, and geothermal activity along the plate boundaries.

16. Evidence for Plate Tectonic Theory Mountain ranges being formed where plates are pushing against each other –EX: the Himalayas

17. Evidence for Plate Tectonic Theory There are ridges, such as the Mid-Atlantic Ridge where plates are separating

18. Pangea http://www.exploratorium.edu/origins/antarctica/ideas/gondwana2.html

19. Summary Lets talk about the main points of what we just discussed.

20. Evidence for Seafloor Spreading During World War II, sensitive instruments called magnetometers were developed to help detect steel-hulled submarines. When research scientists used magnetometers to study the ocean floor, they discovered a surprising pattern. Measurements of magnetic variations showed that, in many areas, alternating bands of rocks recording normal and reversed polarity were arranged symmetrically about mid- ocean ridges

21. Evidence for Seafloor Spreading Magnetic Reversals –The Earth has a magnetic north pole and a magnetic south pole –These poles have flipped periodically in Earth’s past This means the north pole has become the south pole and vise versa. –the record of the reversal of the magnetic field is preserved in magnetic rocks which lie along the ocean floor

22. Evidence for Seafloor Spreading Magnetism in the Earth is created by –Magnetic material –Currents A bar of iron can be made into a magnet by wrapping it with wires and running a current through the wires.

23. Evidence for Seafloor Spreading

29. Summary Lets talk about the main points of what we just discussed.