1. CH 9 Plate tectonics
1915 – Alfred Wegener proposed his continental drift hypothesis
200 mya one large super-continent Pangaea (all lands) began to break up
Panthalassa – all oceans
Not widely accepted b/c he couldn’t explain why it occurred
Dies in 1930 trying to figure it out

2. Evidence Jig-saw puzzle pieces fit Fossil evidence Climatic evidence
SA and Africa
Fossil evidence
Mesosaurus and Glossopteris
Climatic evidence
Glaciers and coal deposits
Rock evidence
Age, type, alignment of mts

3. Plate Tectonics Move slowly about 5 cm or 2.5” per year
Plate movement causes EQs, volcanoes, mts
Lithosphere – plates
outer and rigid
Crust and upper mantle
Moves over the asthenosphere
Asthenosphere
below and plastic like
Lower mantle

4. Boundary Types Transform Divergent Plates slide past one another
Stress involved is shearing
Forms Eqs
Ex: San Andreas Fault
Divergent
Plates move away from each other
Stress involved is tension
Forms mid ocean ridges and rift zones
Ex: Mid-Atlantic Ridge and Iceland

5. Convergent Plates move towards each other
Stress involved is compression
3 different results!
oceanic-continental crusts meet
Subduction (denser plate [oceanic] dives below)
Ocean trench forms offshore
Continental volcanic arcs
Ex: Cascades, Andes

6. Oceanic-oceanic crusts meet
Subduction occurs and one plate dives down
Ocean trench forms
Volcanic island arcs
Ex: Japan, Aleutians
Continental-continental crusts meet
No subduction
Collision boundary
Mountains form
Ex: Appalachians, Himalayas

7. Pie crust meets hand tossed)
Thinner and more sweet
Holds up better to washings
Able to leap tall buildings in a single bound.
Makes Jessica Alba look like a ho.

8. Plate Tectonic Evidence
1. Paleomagnetism
Polar wandering & Polar reversals
2. Earthquake patterns
Earthquakes plate boundaries
3. Ocean Drilling
Glomar Challenger & Harry Hess
180 million (oceanic) vs. 4 billion (continental)
4. Hot spots—example = Hawaii
Only one active volcano
Evidence of movement & direction
Islands further from hot spot are oldest

9. Causes of Plate Motion
Scientists generally agree that convection in the mantle is the basic driving force for plate movement.
The unequal heating within the earth causes this.
Read about slab-pull & ridge-push.
Read about mantle convection.