1. Chapter 8---Plate Tectonics The theory of plate tectonics combines many of the ideas about continental drift (originally proposed in 1912 by Alfred Wegener in Germany) and sea-floor spreading (suggested originally by Harry Hess of Princeton University).

2. Alfred Wegener Anyone who "valued his reputation for scientific sanity" would never dare support such a theory, said a British geologist. The scientific community ridicule the concept that would revolutionize the earth sciences and revile the man who dared to propose it. "Doesn't the east coast of South America fit exactly against the west coast of Africa, as if they had once been joined?" wrote Wegener to his future wife in December 1910. "This is an idea I'll have to pursue." http://www.divesmarts.com/images/alfred_wegener.png

3. Alfred Wegener Evidence Wegener first noticed the similarities in the shoreline of continent on both sides of the Atlantic Ocean, he then began fitting them together. He particularly liked the way in which South America and Africa fit. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

4. Alfred Wegener Evidence Wegener used documented cases of fossil organisms that had been found on different landmass that could not have crossed the current oceans. Fossils of Mesosarus have been found only in South America and Africa. Remains of other organisms appear to link these two continents during the late Paleozoic and mesozoic eras. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

5. Alfred Wegener Evidence The Appalachian Mountains that disappear off the coast of Newfoundland match mountains in the British Isles and Scandinavia which are comparable in age and structure. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

6. Alfred Wegener Evidence The last form of evidence that Wegener use to support his continental drift hypothesis was ancient climates. When the continents are put together to form Pangaea the remains of glacial materials fit together to form a pattern like the large ice sheets that cover our poles today. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

7. Plate Tectonic Theory In this theory the earth is made up of many sections of lithosphere, solid pieces of the earth's crust and upper mantle, that float on top the the asthenosphere. The asthenosphere the a plastic like layer under the lithosphere that has fluid-like properties that can flow. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

9. Each of these pieces of lithosphere are called plates. The picture below shows all of the earth's major boundaries and how they are interacting with each other.

10. BOUNDARY This diagram show the relative motions and features associated with the three types of plate boundaries. Letter A is a divergent boundary in which each plate is moving away from the other. Letter B shows a convergent boundary where two plates are coming together. Finally in letter C, there is the tranform boundary. Here the two plates are sliding past one another. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

11. DIVERGENT BOUNDARY Currently in the northeast section of Africa is a good example of a divergent boundary system. Here rising magma rises upward, causing cracks in the rigid lithosphere. As the cracks pull apart, large slabs of rock sink, creating a rift zone. More spreading creates a narrow sea, like the Red Sea, and eventually a expansive ocean basin and a ridge system like the Atlantic Ocean. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

12. CONVERGENT BOUNDARY An example of continental- continental convergent boundary. The continuous collision of India and Asia, which began about 45 million years ago, produced the majestic Himalayas. Other convergent boundary interactions include oceanic-oceanic, forming a volcanic island arc, and oceanic-continental, forming a continental volcanic arc.. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

13. TRANSFORM FAULT The Mendocino transform fault connects a subduction zone to a divergent boundary by permitting seafloor generated at the Juan de Fuca ridge to move southward past the Pacific plate and under the North American plate. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

14. Testing the Model In the 1950's it was discovered that when iron-rich minerals in lavas cooled, they became magnetized in the direction parallel to the existing magnetic field. Plotting the apparent position of the magnetic north pole over the past 500 million years showed that either the the magnetic poles migrated through time or that the lava flows had moved and the continents had drifted. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

15. MAGNETIC POLARITY It was also noticed that the magnetic polarity of the earth has reversed back and forth throughout it's history. This was a very important piece of evidence for the Plate Tectonic Theory. When looking at the polarity of the rocks on the ocean floor. The polarity went from normal to reversed in alternating bands creating a mirror image on both sides of the mid-ocean ridge. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

16. EARTHQUAKES Another piece of evidence was the the distribution of shallow, intermediate, and deep-focus earthquakes. A close look will show that deep-focus earthquakes only occur in association with subduction zones. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

17. HOT SPOT The final bit of supporting evidence is the information that scientists get from hot spots. For example, the Hawaiian Island and the seamounts that extend from Hawaii to the Aleutian trench show the movement of the Pacific plate as it moved over the hot spot. Radiometric dating shows that the volcanic activity decreases in age toward the island of Hawaii, which is now over the hot spot. http://www.gasd.k12.pa.us/~dpompa/Mini%20Lecture.html

18. The images below show how Pangaea broke up and moved the continents to their current locations. Pangaea

19. Driving Mechanism First is the idea that large convection cells in the mantle carry the slabs of lithosphere in a conveyor-belt manner. Second, is the idea that because a subducting slab is more dense than the underlying material that it pulls the plate down. This is called slab-pull. Also because of gravity, the elevated portion of the plate at a ridge crest the plate is pushed along. This is called slab-push. Finally, the hot plume method is the idea that upward convection is occuring only in a few large plumes, while dense subducting plates complete the cell.

20. CITED http://www.gasd.k12.p a.us/~dpompa/Mini%2 0Lecture.html

21. SUMMARY 1. List the evidence that Wagner used to make the case for Continental Drift? –A. ______________________________________________________________ –B.______________________________________________________________ –C. ______________________________________________________________ –D. _____________________________________________________________ 2.How do solid plates move? 3. Draw a divergent boundary. 4. Draw a convergent boundary. 5.Draw a transform fault. 6. How does magnetic polarity help prove Plate Tectonics? 7. What is a Hot Spot? 8. What is the driving mechanism for Plate Tectonics?