1. Continental Drift Theory of Alfred Wegener
Thought the continents fit together like puzzle pieces.
All continents were once one big continent called Pangaea (means = all land)
Similar rocks and fossils are found on widely separated continents.
Pangaea broke apart and slowly moved into current positions.
No one believed this until Hess came up with the theory of seafloor spreading to explain how continents moved.
Fossil, Rock, climate clues (glacial deposits in Africa, etc.) are proof of this.

2. Pangaea

3. Plate Tectonics
Evidence of plate movement can be seen at plate boundaries and rift valleys.
Plates are pieces of crust and upper mantle (Lithosphere).
Plates float on plastic-like layer of mantle called the Asthenosphere.
Convection currents start in mantle. Hot stuff rises, spreads out, cools, then sinks.

4. Plate Boundaries
Where they collide we get mountains, volcanoes, and ocean basins.
Indo-Australian Plate + Eurasian Plate = Himalayas. No earthquakes there because mountains just crumple up.
Ocean + Ocean = Japan
Ocean + Continental = Andes
Divergent – move apart (Rift Valleys)
Slide past = transform = earthquakes

5. Plate Boundaries

6. Seafloor Spreading Proposed by Harry Hess
Evidence is based on magnetism and age evidence.
Youngest rocks are at mid-ocean ridges.
Ocean rocks are younger than continental rocks.
Magnetic field in iron-bearing rocks has reversed in a steady pattern.
Glomar challenger has taken rock samples showing how age of rocks gets older the farther you get from mid-ocean ridge.
Magma comes up, forces plates apart, cools, and spreads out. (convection current).
This Photo by Unknown Author is licensed under CC BY-SA

7. Mid-Ocean Ridge

8. This Photo by Unknown Author is licensed under CC BY-SA