1. Structure of the Earth and Plate Tectonics Notes

2. Structure of the Earth

3. 1. Crust: outermost layer Ranges from 5 to 100 km thick We know the most about this layer!

4. Structure of the Earth Two types of crust: Continental: less dense; averages 30 km thick Oceanic: more dense; averages 5-8 km thick

5. Structure of the Earth 2. Mantle: middle layer About 2900 km thick

6. F. Y. I. Scientists know this through observations of: 1.The ocean floor, where magma escapes 2.Faults where mantle rock has been pushed to the surface

7. Structure of the Earth 3. Outer Core: liquid layer of the Earth About 2200 km

8. Structure of the Earth 4. Inner Core: solid, dense center of the Earth About 1200 km

9. Plate Tectonics

10. Continental Drift Proposed by Alfred Wegener in 1912 Continents are moving!

11. Continental Drift Evidence in 1912 includes: 1. Fit of continents 2. Similarity of fossils across oceans

13. Continental Drift Rejected at the time because there was no understanding of a force strong enough to move continents Continental Drift animation Essentials of Geology : Chapter 2 : Animations

14. Continental Drift Wegener died in 1930 No change in thought until the 1950’s

15. Continental Drift More evidence: 3. Seafloor spreading 4. Magnetic reversals

16. Sea-floor spreading Process by which new oceanic crust is created at mid-ocean ridges

17. Sea-floor spreading Mid-ocean ridge is where the ocean floor is “torn apart” http://www.wwnorton.com/earth/egeo/animations/ch2.htm

18. Younger rock Older rock

19. Sea-floor spreading Older rocks are found near continental shelves, younger are found along the mid- ocean ridge

20. Magnetic reversals Process by which Earth’s north and south magnetic poles periodically change places

21. Magnetic reversals Scientists generally agree that the Earth's magnetic field reverses itself on the average of once every 500,000 years. Widespread evidence suggests that the last reversal occurred 700,000 years ago. http://www.wwnorton.com/earth/egeo/animations/ch2.htm

22. Magnetic reversals The existence of magnetic reversals in the Earth's past is generally accepted by scientists. Nobody has a really good explanation for why it happens. It probably has to do with the solid inner core of the earth rotating within the liquid outer core.