Plate Tectonics

1. Plate Tectonics

4. Continental Drift • Alfred Wegener suggested all earth’s land masses collided 300 million years ago to form one supercontinent • He named it PANGAEA.

5. Pangaea

6. Wegener’s Proofs #1 and #2 1. He saw a jigsaw fit between South America and Africa 2. Fossils of the same plants and animals on both continents.

7. Wegener’s Proof #3 Mountains of similar age and structure on both sides of the Atlantic Ocean

8. Wegener’s Proof #4 • There is proof that ice sheets had once covered the southern portions of South America, Australia, India and Africa 300 million yrs ago. Glaciers could have only formed if the continents were together. • However, theory was debated because scientists wanted evidence to explain movement of continents.

9. Missing Proof • Wegener could not explain what mechanism was powerful enough to move huge continents • Scientists never believed him • By the 1930’s Wegener’s work was largely ignored

10. J. Tuzo Wilson • Wilson (Canadian) sparked new interest in continental drift theory. • Now known as plate tectonics (includes more than just continents, also includes ocean plates)

11. Plate Tectonics • Theory that helps explain most geologic processes. • Earth’s shell is made up of approximately 20 plates (continents and oceans) • Plates moving over a weak layer of hot rock measured by strain gauges and satellite measurements • Perhaps caused by uneven distribution of heat within the earth, causing convection currents.

12. Plate Tectonics & Convection Currents • Theory of Plate Tectonics offered a more scientifically sound explanation for the movement of continents. • Plate Tectonics is the movement of the earth’s surface which is divided into 6 major plates. Within each major plate, there are numerous sub-plates as well. • Large convection currents in the mantle cause plates to move (hot liquid rises toward earth’s surface – moves along earth’s surface – cools and comes back down toward mantle – causes mantle rock to shift)

13. Convection Currents

14. Convection Currents

15. Plate Movements • Convergent Boundaries • Divergent Boundaries • Transform Boundaries

16. Convergent Plate

17. Convergent

18. Divergent Plate

19. Divergent • A divergent plate boundary is when two tectonic plates are moving away from each other • Mostly occur between two oceanic plates, creating oceanic ridges • Found in the middle of the Atlantic Ocean (mid-Atlantic Ridge) New land is created by volcanic activity.

20. Divergent

21. Transform

22. Transform • Plates slide past one another and no new lithosphere is created or destroyed • Found in California (San Andreas Fault). • Earthquakes are produced.

23. Transform - Earthquakes • Less than 3.5 Generally not felt, but recorded. • 3.5-5.4 Often felt, but rarely causes damage. • Under 6.0 At most slight damage to well-designed buildings. • 6.1-6.9 Can be destructive in areas up to about 100 kilometers across. • 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. • 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

24. The Types

25. Ring of Fire • ↑ of tectonic plate activity • 75% world’s active volcanoes • 90% world’s earthquakes; 80% world’s largest earthquakes