1. THE LANGUAGE OF THE EARTH – PART IV PLATE TECTONIC THEORY: THE EVIDENCE

2. Rock Cycle

3. Alfred Wegener 1880-1930 1915 – The Origin of Continents and Oceans (3rd edition, 1922) Meteorologist by training Introduced the hypothesis of Continental Drift Postulated the existence of the supercontinent Pangea Evidence: Fit of the continents Fossil record Similar geologic structures Similar paleoclimates

4. Fit of the Continents Wegener’s 1915 Reconstructions ~250 Ma

5. Fossil Evidence

6. Similar Geologic Structures Wegener’s Sketch (1931)

7. The Appalachian-Caledonian Mountains ~250 Ma

8. Paleoclimate Evidence ~300 Ma

9. General Dismissal of Wegner’s Theory an amateur (not even a geologist!) inadequate driving mechanism for horizontal motion of continents (tidal energy, earth’s rotation) uncertainty about the seafloor and earth’s mantle some supporters: DuToit (South Africa), Holmes (England), but many more detractors especially in the US from J. Holden Continental Collapse Continental Drift (Wegner) Continental Drift and Seafloor Spreading

10. Paleomagnetism: New Evidence for Continental Drift in the 1950’s Declination – azimuth direction to the magnetic pole Inclination – angle that magnetic field is tilted into the earth

11. Apparent Polar Wandering

12. Investigations of the Seafloor The Final Pieces of the Puzzle

13. Earthquakes, Volcanoes, Ocean Ridges, and Ocean Trenches Earthquakes VolcanoesOcean Trenches Ocean Ridges

14. Benioff Zones Sites of Ocean Floor Subduction and Melting

15. Seafloor Spreading An “essay in geopoetry” by Harry Hess (1961)

16. Magnetic Striping of the Seafloor Confirmation of the Seafloor Spreading Hypothesis Vine and Matthews (1963)

17. Further Confirmation Youth of the Ocean Crust

18. Continental Drift + Seafloor Spreading = Theory of Plate Tectonics (late 1960’s)