1. Continental Drift Seafloor Spreading Plate Tectonics Theory

2. Continental Drift Early evidences: Fit of continents
Mountain ranges and rock sequences
Unique organisms
Glacial debris
Present
200 million years ago

3. Continental glacier on Pangaea
Current location of glacial debris

4. Rock Magnetism Wegener’s ideas put on shelf for a while
New magnetism measurement techniques in mid-20th century
Expected some wobble of magnetic pole

5. Compared magnetism on distant continents
Compare rocks of same age on distant continents
Found significant drift of pole
Found more than one magnetic pole at same time?
Confirmed that drift must be occurring

6. Another discovery from magnetism
Reversals!
No explanation, but real

7. To the seafloor……Ideas of Harry Hess
Location of mid-ocean ridges, deep sea trenches
age of seafloor

8. Hess’s ideas Took philosophical approach
Explained age by production of new seafloor at ridges and destruction at trenches
“Introduced” idea of convection in the mantle
Called seafloor spreading

9. Hess’s vision
Trench
Ridge
Trench

10. Seafloor spreading – version 2
Vine, Matthews, Morley
Observed magnetic pattern on seafloor
Finally noticed symmetry of pattern
Testable prediction

11. Magnetic pattern
from magnetometer
Note symmetry about ridge;
seafloor colored by artist

12. Formation of seafloor magnetic pattern

13. Another “view” of seafloor magnetic pattern

14. Other evidences of seafloor spreading
Chains of islands and ages
Development of types of coral reefs
Satellite imagery

15. Chains of islands and their ages

16. Location of hot spots (mantle plumes)

17. Basic theory of plate tectonics
Remember layering of earth
Lithosphere broken into pieces called plates
Plates move and interact at boundaries
Find boundaries with earthquakes and topographic features

18. Earthquakes (about 10 years)

19. Plates (puzzle pieces)

20. Plate Boundaries Divergent : mid-ocean ridge Convergent:
oceanic-continental
oceanic-oceanic
Transform faults:
offsets in
mid-ocean ridges

21. Divergent and transform boundaries

22. Convergent boundaries
Oceanic-continental
(top picture)
Oceanic-oceanic
(bottom picture)