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

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

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

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

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

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

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.

Plate Tectonic Evidence 1. Paleomagnetism Polar wandering & Polar reversals 2. Earthquake patterns Earthquakes occur @ 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

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.