17.3 & 17.4 Notes Continental Drift

1. 17.3 & 17.4 NotesContinental Drift • Main Points: The theory published by Wegner states that the continents were once all connected and they continually drifted apart.

2. Pangaea • Explain: A super-continent believed to exist about 200 million yrsago. Look at a world map & the continents seem to fit together like a jigsaw puzzle.

3. Dinosaur Fossils Explain:Fossils from the same dinosaur (Mesosaurus) exist in both S. America & S.W. Africa. Evidence Against Wegner’s Pangaea Theory: Another popular theory said that land bridges formed between continents, explaining how Mesosaurus got back & forth.

4. Other Fossil Examples

5. Full Dinosaur Skeleton Found in Alaska, Plus Photos of Rare Dinosaur Fossils July 2011 TongassNational Forest http://www.ibtimes.com/full-dinosaur-skeleton-found-alaska-plus-photos-rare-dinosaur-fossils-835539

6. Dino Tracks in Alaska, 2013 Yukon River 9 min video http://www.youtube.com/watch?v=nNGX2LhK5pI

7. Glaciers • Explain: Evidence of glaciers was found in hot, dry Australia.

8. Tropical Plant Fossils Explain: Fossils of tropical plants were found in non-tropical regions

9. Arthur Holmes’s Evidence1944 • Describe: Holmes stated that convection within the mantle could move continents.

10. Technological Evidence • Describe: Scientists found very young rocks on the ocean floor & evidence of the ocean floor spreading & magnetic striping.

11. Earths Mechanical LayersLithosphere Structure: Mostly solid rock Location: Top layer, includes continents & ocean floor. Thickness=few km-250 km under mountains. Describe Movement: Lithosphere is broken into 7 major plates that move atop the asthenosphere.

12. Asthenosphere Structure: Deformable rock Location: Found under lithosphere & above mesosphere. Makes up large portion of upper mantle. Average depth = 400-700 km. Describe Movement: Due to convection.

13. Mesosphere Structure: Nearly solid because of high pressures Location: Lower mantle Describe Movement: Influences convection in the mantle, so it indirectly leads to movement of the plates.

14. Transform Boundaries Describe: Where 2 plates slide past each other & creates earthquakes. Structures Created: Faults (ie.SanAndreas fault).

15. Divergent Boundaries Describe: The location where 2 plates move apart from each other. Structures Created: Oceanic ridges. Rifts are formed where ridges split apart.

16. Convergent Boundaries Describe: Where 2 plates smash into each other.

17. Structures Created by Convergent Boundaries • Oceanic/ContinentalBoundaries: Denser oceanic crust goes beneath continental crust & gets destroyed at the “subduction zone”. As oceanic crust melts, it bulges the continental crust & creates volcanic mountains!

18. Structures cont. • Oceanic/Oceanic Boundaries: When 2 oceanic plates collide; forms volcanic island arcs as the denser, older crust sinks below lighter, younger crust. Each island arc also has a trench.

19. Structures cont. • Continental/Continental Boundaries: When 2 continental plates collide; forms mountain ranges.

20. Convection Currents Model Describe: The mantle moves due to convection, dragging the lithosphere along. Slab-Pull Describe: As plates collide, some crust is subducted& pulls the rest of the crust along with it.

21. Slab-Push Describe: A movement caused by the force of magma pushing its way up between 2 plates.

22. Hot Plume Describe: Columns of magma rise from lower mantle; causes plate divergence & creates hot spots (long-lived volcanoes).