1. Warm-up #43 Mar. 26  Brainstorming: Will California eventually slide into the ocean? Have continents really drifted apart over the centuries?

2. Unit 8

3. Continental Drift  Alfred Wegener – German scientist proposed the theory of continental drift.  This hypothesis stated that the continents had once been joined to form a single supercontinent  Pangaea – all land

4. Pangaea  Part of Wegener’s theory was that Pangaea started splitting into smaller continents 200 million years before  Wegener collected lots of evidence to prove this theory

5. The Continental Puzzle  The shorelines of the continents nearly fit together to make a large land mass.  HOWEVER  The shorelines are constantly eroding and changing.

6. Matching Fossils  Fossil evidence for continental drift includes several fossil organisms found on different landmasses.  At one point the theory was that there were land bridges, however there is no evidence of this.

7. Rock Types and Structures  Several mountain belts that end at one coastline reappear on a landmass across the ocean

8. Ancient Climates  Wegener found glacial deposits showing that between 220 million and 300 million years ago ice sheets covered large areas of the S. Hemisphere

9. Rejecting Wegener’s Hypothesis  Many scientists questioned Wegener’s theory  He could not describe a mechanism that was capable of moving the continents  There was not enough evidence

10. A New Theory  In 1968 a new theory was proposed – PLATE TECTONICS

11. Plates  The lithosphere is broken up into segments called plates  The lithosphere is the uppermost layer of the mantle  Plates continuously move and change shape and size

12. Warm-up #44 Mar. 27  Mesosaurus provided evidence that South America and Africa were once joined  On average, how much do you think the plates move a year?  5 centimeters

13. Plate Boundaries  A plate boundary is where two plates meet.  There are three main types of boundaries: Divergent Convergent Transform fault

14. Divergent  Also called spreading boundaries  Occurs when two plates move apart  Results in upwelling of material from the mantle to create new seafloor

15. Convergent  Form where two plates move together  Results in lithosphere plunging beneath an overriding plate and descending into the mantle

16. Transform fault  Margins where two plates grind past each other without the production or destruction of lithosphere

17. What happens at boundaries?  Divergent Boundaries Seafloor spreading occurs along the boundary Forms fractures on the ridge crests Fractures fill with molten material When the boundary occurs on a continent, rifts or rift valleys form

18. Convergent Boundaries  Oceanic-continental boundary Forms a subduction zone within Volcanic arcs form  Oceanic-oceanic boundary Often forms volcanoes on the ocean floor Island arc forms as volcanoes emerge

19. Convergent Boundaries  Continental-continental boundaries Neither plate will subduct Can produce mountains

20. Transform Fault Boundaries  No new crust created  No crust is destroyed  Most are in oceanic crust  Parallel the direction of plate movement  Aids movement of crustal material

22. Boundary Brochures  Needs to include: 3 types: Divergent, Convergent, Transform What each one is (use your notes) A picture for each An example for each ○ http://geology.com/plate-tectonics.shtml http://geology.com/plate-tectonics.shtml Needs to be colored

23. Warm-up #45 Mar.28 Brainstorming:  Do you think it is possible for Earth’s magnetic poles to be reversed?  If so, what do you think could happen to the biosphere?  Also, how might geologist use that to support plate tectonics?

24. Evidence for Plate Tectonics  Paleomagnetism Most persuasive piece of evidence. Ancient magnetism preserved rocks. Paleomagnetic records show: ○ Polar wandering ○ Earth’s magnetic field reversals

25. Evidence for Plate Tectonics  Earthquake patterns Associated with plate boundaries Deep-focus earthquakes along trenches provide a method for tracking the plate’s descent

27. Evidence for Plate Tectonics  Ocean Drilling Deep Sea Drilling Project – Glomar Challenger Age of deepest sediment ○ Youngest are near the ridges ○ Older are at a distance from the ridge Ocean basins are geologically young

28. Evidence for Plate Tectonics  Hot Spots Rising plumes of mantle material. Volcanoes can form over

29. Driving Mechanism  No one model explains all plate motion  Earth’s heat is the driving force  Several models have been proposed Convection currents in the mantle Slab-pull and slab-push model Hot plumes

30. Dynamic Earth  http://www.learner.org/inte ractives/dynamicearth/inde x.html

31. Ticket out the Door 1. What are the 3 main types of plate boundaries? 2. Name 2 pieces of evidence Wegener used to prove continental drift. 3. What is type of boundary is this?