Warm-up #43 Mar. 26

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 Plate Tectonics

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 • 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/interactives/dynamicearth/index.html

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