Theory of plate tectonics

1. Theory of plate tectonics

2. Continental drift hypothesis • Before the theory of plate tectonics in the 1960’s, there was Alfred Wegener’s hypothesis of continental drift. • He thought all the continents were once connected to make a single supercontinent called Pangea.

3. Pangea 300 million years ago

4. Evidence that supported Pangea

5. Why do the continents move? • The theory of plate tectonics states that the Earth’s lithosphere is broken up into plates. These plates continually move and change shape and size. • When plates move, they cause earthquakes and volcanoes along the plate boundaries. • Plates move slow-on average 5 cm a year! • Plate motion is caused by convective currents in the asthenosphere

7. Types of plate boundaries • Divergent- plates pull apart • Real life example: atlantic ocean and east african rift valley • Causes: earthquakes, sea floor spreading, rift valleys, and mid ocean ridges

8. Mid ocean ridge East African rift valley divergent

9. Convergent continental continental • 2 continents collide-push together • Example: how Appalachian mountains formed and the Himalayan mountains • Causes earthquakes and mountains

10. Appalachian mountains form Himalayan mountains

11. Convergent oceanic oceanic • 2 ocean plates collide-push together • Example: islands of japan, indonesia • Causes: earthquakes, subduction zones, tsunamis, volcanic islands

13. Convergent oceanic continental • An ocean plate and continental plate collide • Examples: Cascade volcanic mountains in northwestern US (Mt st Helens) • Causes: earthquakes, volcanic eruptions, tsunamis

15. Transform fault • 2 plates slide past each other • Example: San andreas fault in California • Causes only earthquakes

17. What evidence supports the theory of plate tectonics? • Paleomagnetism- alternating layers of rock at the bottom of ocean floors show normal and reverse polarity

18. Earthquake patterns

19. Hot spots