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Plate Tectonics
Continental Drift
I Alfred Wegener 1915
A. Super continent =Pangaea, What he used to prove his theory
1. Puzzle fit of continents
2. Fossils
A .mesosauras (animal)
B. glossopteris (plant =fern)
3. Mountain Types/ Rock Record (same age and composition)
4. Evidence of similar climates and glaciers
5. Other evidence
a. Coal deposits
b. Coral reefs
B. Idea was dismissed because- He didn’t have the mechanism to prove how it worked
C. Renewed Interest in 1950
1. Sea Floor Spreading - Harry Hess
a. Mid Atlantic ridge
2. Paleomagnetism
E. Types of Plate Boundaries
1. Divergent= dividing plates
a. Mid Atlantic Ridge
b. Red Sea
c. East African Rift Zone
2. Convergent= plates colliding
a. Continent to continent – India / Eurasia
b. Continent to ocean- N and S. America / Pacific Coast
c. Ocean to ocean = Volcanic islands = Indonesia, Japan, Philippines
3. Transform = sliding side by side in opposite directions- Often associated with the
Mid Atlantic Ridge
Example: San Andreas Fault line in California
F. 1968= Plate tectonics (Name change because the ocean crust moves as well as the
continents))
G. Mechanism that moves the plates? Convection Currents occurring in the mantle- heat
From the radioactive core rises
II Seismic Waves
A. Types
1. Primary or P Waves, Push and pull, fastest seismic wave, travels thru solid &
liquids
2. Secondary waves or S Waves, side to side, destructive, passes only thru solids
3. Surface Waves, Long Waves or L waves slowest, roll along the surface
B. Seismic waves change speed when they reach the crust/mantle boundary = Moho
1. S waves due not travel through the outer core, therefore it must be a liquid