What is Plate Tectonics Theory?

1. What is Plate Tectonics Theory? Use this part of the PPT for p. 7 of your INB!!!

2. The Discovery of Plate Tectonics A. Continental Drift (Alfred Wegener) Proposed large-scale movement of the continents

3. Evidence: 1. “Puzzle fit” of continents to form “Supercontinents” a. Suess (1900)-Gondwana b. Wegner (1915)-Pangea

4. More Evidence… 2. Similar rock ages 3. Similar geologic structures such as mountain ranges 4. Fossil Evidence from the Mesosaurus 5. Climate Evidence such as glacial deposits **Wegener’s theory did not gain much support because he could not explain how the tectonic plates move

5. B. Seafloor Spreading- Henry Hess) • Convection currents move plates around • Mantle source of heat and convection • proposed new and recycled seafloor 4. Evidence from submarines during WWII around the Mid-Atlantic Ridge showed the seafloor is a mirror image on each side of the ridge **There was no evidence for this theory, until…

6. Magnetic Pole Reversals or “Tape Recording” 1. Magnetic Reversals • Switching strength to the south from the north • Preserved in lava because iron points towards stronger pole • Age of these iron bands can be calculated and if the seafloor is spreading from a center, they should be mirror images on each side of ridge

7. (continued) • Seafloor ages • Speed = distance / time

8. Mid-ocean ridge Million years ago (Ma) 4.0 3.0 2.0 Ocean crust today 5.0 3.3 2.5 0.7 0 0.7 2.5 3.3 5.0 million years old

9. Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. Mid-Atlantic Ridge High intensity Low intensity

10. Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. A sensitive magnetometer records magnetic anomalies,… Mid-Atlantic Ridge High intensity Low intensity

11. Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. A sensitive magnetometer records magnetic anomalies,… Iceland Mid-Atlantic Ridge Mid-Atlantic Ridge High intensity Low intensity

12. Magnetic mapping can measure the rate of seafloor spreading An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern. A sensitive magnetometer records magnetic anomalies,… …alternating bands of high and low magnetism. Iceland Mid-Atlantic Ridge Mid-Atlantic Ridge High intensity Symmetrical bands on both sides. Why? Low intensity

13. Looking at pole reversals preserved in the ocean floor provides the evidence needed to support seafloor spreading. Seafloor spreading provides the mechanism for “how” the continents move! (Wegener)

14. A Mosaic of Plates • Entire Earth’s surface is made up of tectonic plates • Made up of a special layer of the Earth called the lithosphere and “ride” on top of the mantle • Plates have both oceanic crust & continental crust • Continental crust is less dense than oceanic crust

15. A Mosaic of Plates (cont.) • Specific Geologic activities that occur along plate boundaries or because of plate movement: • Volcanoes • Mountain building • Earthquakes • Hot spots • Faults/cracks in crust