1. The Theory of Continental Drift Observations Leading To and Evidences Supporting Theory

2. You will… Fill in blanks/notes Fill in the observations to support the theory Label the observations to support the theory on your diagram (by color coding) Label a diagram showing sea-floor spreading and the magnetic reversals recorded in the rock as the sea-floor spread

3. Theory of Continental Drift Continental Drift is the theory that the CONTINENTS can DRIFT apart from one another and have done so in the past.

4. Observations Remember: A theory is a unifying explanation for several observations that has been supported by testing Alfred WEGENER developed his theory that the continents can drift and have done so in the past based on the following observations:

5. Observations Shape/“Fit” of the continents The continents appear as if they could fit together like jigsaw puzzle pieces!

6. 1. Shape/“Fit” of Continents PANGAEA 245 million years ago!

7. Observations Fossils of the same plant and animal species found on continents separated by oceans These organisms could not have made it across the Atlantic Ocean! The pattern of fossil findings is hard to explain unless at one point these continents were not separated by an ocean!

8. 2. Same Fossils on Different Continents Question: Would you expect to find the same organisms on different continents? For example, would you expect to find the same organisms in Africa and Antarctica? Why or why not?

9. Observations Same rocks on different continents Rocks that were formed at the same time under the same conditions with the same composition are found on continents separated by oceans

10. 3. Same Rocks on Different Continents This pattern is hard to explain unless at one point these continents were together as one!

11. Observations Same ancient climatic conditions are found on several continents The climate of a continent depends upon its location on the Earth relative to the sun. Ex. Equator = Hot; Pole = Cold Evidence of similar climates on continents in very different locations on Earth is hard to explain unless…

12. 4. Same Ancient Climate on Different Continents …. at one point these continents were together as one!

13. Critics Many scientists did not accept Wegner’s theory of Continental Drift; they said the continents cannot “plow through” the oceanic crust because oceanic crust is much denser than continental crust, and objects with less density cannot push through objects with higher density.

14. So, what force could move entire continents? 1. SEA-FLOOR SPREADING -the process by which new oceanic crust forms at the mid-ocean ridge. Evidences to Support Theory

15. Sea-floor spreading was discovered when scientists noticed the pattern of younger rocks at the mid- ocean ridges and older rocks farther away from the ridges.

16. Evidences to Support Theory When tectonic plates move away from each other magma rises to fill the gap, cools and hardens creating new oceanic crust. Scientists finally knew why the continents move! The sea-floor spreads as plates move away from each other! Sea-floor Spreading causes

17. Evidences to Support Theory 2. Magnetic Reversals are recorded in the crust as the sea-floor spreads.

18. Earth’s Magnetic Field The Earth is a giant magnet! Every ~700 thousand years the Earth’s magnetic North and South poles change places. Will a magnetic reversal occur sometime soon?

19. Tiny grains of magnetic minerals in molten rock will align with Earth’s magnetic field. When the rock cools and hardens the Earth’s magnetic signature at that time is recorded in the rock. Evidences to Support Theory THIS IS FURTHER PROOF THAT THE SEA- FLOOR SPREADS, OR THAT NEW CRUST IS CREATED OVER TIME THERE IS A “TIME STAMP” OF EARTH’S MAGNETIC FIELD IN THE ROCK

20. You should have… Filled in the blanks/notes Filled in the observations to support the theory Labeled the observations to support the theory on your diagram You now need to… Study Figures 5 & 6 on pp. 458- 459 of Sea-floor Spreading & Magnetic Reversals Label the diagram showing sea- floor spreading and the magnetic reversals recorded in the rock as the sea-floor spread

21. Sea-Floor Spreading

22. Magnetic Reversals

23. Pangaea Sea-floor SpreadingMagnetic Reversals