1. Earth’s Interior Layers and Continental Drift

2. Objectives Review Earth’s layers Summarize Wegener’s hypothesis Describe the process of sea-floor spreading Identify how paleomagnetism provides support for the idea of sea-floor spreading Explain how sea-floor spreading provides a mechanism for continental drift.

3. Earth’s Interior: Physical properties

4. Based on Composition (What each layer is made of) Crust – solid, relatively low density silicate rock Mantle – Semi fluid, denser, mafic (iron and magnesium bearing) rocks Core – Liquid then solid iron and nickel with traces of heavier elements

5. Based on Structure(physical properties) Lithosphere – rigid Aesthenosphere – plastic Mesosphere – rigid Outer core – liquid Inner core - rigid

6. Warm-Up Question What does continental drift mean?

7. Wegener’s Theory Alfred Wegener proposed a theory that continents can drift apart from one another and have done so in the past ….known as Continental Drift

8. claimed that present day continents once made up a single land mass or supercontinent …known as Pangaea

10. Evidence of Continental Drift 1.Coastline similarities

11. Evidence of Continental Drift 2.Fossils Similar plant and animal fossils found on both sides of Atlantic Ocean

12. Evidence of Continental Drift 3.Rock Formations Rocks and mountain ranges found in continents separated by oceans are identical

13. Evidence of Continental Drift 4.Climates Glacial rock/debris was found in areas that today have warm climates

14. Why was Wegener’s theory rejected? He could not come up with a proven reason for why the continents did move His theory was not accepted until when geologists had more technology to help them map the ocean floor

15. Mapping of the ocean floor Used sonar to do this

16. What was found on the ocean floor… 1.Trenches Long valleys found along the edge of ocean basins

17. What was found on the ocean floor… 2.Mid-Ocean Ridges Long chains of underwater mountains Usually have a rift valley located at the center

18. Mid-Atlantic Ridge

19. What was going on at the mid-ocean ridges? Sea-floor Spreading New ocean floor forms from cooling lava in the rift valleys The sea floor then slowly moves out underneath ocean Will eventually sink back into Earth’s mantle at trenches

20. Sea-Floor Spreading

21. Evidence of sea-floor spreading Age of the ocean floor Age of ocean floor increases as you move away from ridges

22. Evidence of sea-floor spreading Magnetic reversals

23. Understanding Magnetic Reversals

25. Lava cools, lithospheric igneous rock forms… Many igneous rocks contain the mineral magnetite and the element iron… This causes the rocks to be magnetized = grains align in the same direction as Earth’s magnetic field Geologists know when these reversals occurred, so they can determine the age of the ocean floor

26. Magnetic Symmetry Our final piece of evidence is the magnetic record of the ocean floor. This shows the pattern of reversal and we find a near perfect mirror image on opposing sides of the ridge

27. Summary Question What was the proof that was found that supported Wegener’s theory of continental drift?

28. Homework Read Page #’s 239 – 246 Answer Question #’s 1 - 8