1. Are Continents “Drifting”?
YES
Evidence - Earth’s highest point is rising
(Mt Everest)
America moving from Africa 2-3 cm/yr
Hawai’i migrating 8-9 cm/yr

2. Continental Drift Who developed the theory? Alfred Wegener
Meteorologist

3. Continental Drift What is Continental Drift?
Earth’s continents were once connected into a supercontinent Pangaea
It began to break up about 280 million years ago
They continue to move

4. Continental Drift What are the early observations?
What is the evidence?
Matching coastlines (1500s)
Puzzle-like fit of S America/Africa
& Europe/N America

5. Continental Drift Distinctive rock type on widely scattered continents
Distinctive geologic structures (mountains)
What is the evidence?

6. Continental Drift Same land-dwelling plants and animals
Mesosaurus
Glossopteris
Lystrosaurus
What is the evidence?

7. Continental Drift What is the evidence? Coal deposits in Antarctica
Glacial deposits in Africa, India, Australia & South America

8. Continental Drift Why rejected?
Could not explain what caused the continents to move – “What force could be strong enough to move continents over such large distances?”
Continents would fracture if pushed through the ocean floor

9. Plate Tectonics What is Plate Tectonic Theory?
Earth’ crust and upper mantle is broken into large slabs called plates that move in different directions and at different rates over Earth’s surface

10. Plate Tectonics Sea Floor Spreading What is the evidence?
First proposed by Harry Hess
What is the evidence?

11. Plate Tectonics What is Sea Floor Spreading?
The process by which new oceanic crust is formed by the upwelling of magma at mid-ocean ridges.

12. Plate Tectonics Evidence for Sea Floor Spreading?
Mid-Ocean Ridges – huge underwater mountain chains
Deep sea trenches – deep chasms

13. Plate Tectonics Evidence for Sea Floor Spreading?
Age of rocks – youngest near ridges, oldest farther away
Highest heat flow near ridges
Elevation highest near ridges
Ocean sediment thinnest near ridge

14. Plate Tectonics Evidence for Sea Floor Spreading?
Symmetrical magnetic patterns on opposite sides of a ridge

15. Plate Tectonics Evidence for Plate Tectonics?
Patterns of earthquakes and volcanoes
Locations associated with plate boundaries

16. Causes of Plate Motion Causes Mantle convection
Hot mantle rises, cool mantle sinks
carrying the plate with it as it convects
Convection – transfer of heat by moving fluids

17. Causes of Plate Motion Causes Ridge Push
Uplifted ridge produces a slope
the older, denser lithosphere slides down the slope away from the ridge toward the trench formed at a subduction zone

18. Causes of Plate Motion Causes Slab Pull
Denser, heavier plate subducts beneath less dense plate
pulls the rest of the plate with it,
eventually dragging trailing plate into a subduction zone