Download Chapter 12 Plate Tectonics

Chapter 12 Plate Tectonics
I. Drifting continents
A. Continental drift
1. Theory proposed by Alfred Wegener
2. Earth a single land mass
3. Broken up into large pieces
4. Pangaea
B. Evidence from fossils
1. Support Wegener's theory
2. Glossopteris fossil
C. Evidence from rocks
1. Supports Wegener's theory
2. Deposits left behind by moving sheets of ice
3. Rock formations
II. Spreading ocean floor
A. Midocean ridges
1. Single largest mountain chain
2. Volcanic activity
3. Lava forms new ocean floor
4. Movement of floor also moves continent
B. Transform faults
1. Thin cracks in straight ridge
2. Moving blocks of rocks jam instead of sliding smoothly
C. Age of rocks
1. Young rocks next to midocean ridge
2. Oldest rocks farther away
D. Magnetic stripes
1. Record history of Earth's magnetism
2. Magnetic poles tend to reverse themselves
3. Pattern of stripes provides evidence
E. Destruction of ocean floor
1. Trenches are deepest part of ocean floor
2. Subduction occurs
3. Crust remains the same size
a. New rocks form
b. Old rocks move into trenches
c. Rocks melted by heat of Earth
III. Earth's moving plates
A. Theory of plate tectonics
1. Links continental drift and ocean-floor spreading
2. Explains evolution of Earth
3. Explains formation, movements, collisions, and destruction of crust
B. Lithospheric plates
1. Topmost part of solid Earth
2. Usually contain both continental and oceanic crust
3. Seven major plates
a. Pacific (the largest)
b. North American
c. South American
d. Eurasian
e. African
f. Indo-Australian
g. Antarctic
4. Plates move at different speeds and different directions
C. Plate boundaries
1. Divergent boundaries
a. Occur at midocean ridges
b. Plates move apart
c. Constructive boundaries
2. Convergent boundaries
a. Has trenches
b. Plates come together
c. Collision causes tremendous pressure and friction
d. Produce volcanoes
3. Strike-slip boundaries
a. Formed by lateral faults
b. Plates grind together, slip past horizontally
c. Conservative boundary
D. Plate motion
1. Convection current
a. Movement of material caused by differences in temperature
b. Denser mantle near crust cools and sinks
c. Hotter material pushed up
d. Circular motion moves lithosphere
2. Convergent plates at trenches
a. Denser plate is subducted
b. Other plate floats over it
3. Plate collisions
a. Oceanic and continental plates
1.) Continental (less dense) overrides oceanic
2.) Oceanic plate subducted into trench
b. Two oceanic plates collide
1.) Older plate subducted and melts
2.) Molten rock rises
3.) Volcano forms
c. Two continental plates collide
1.) Edges fold upward
2.) Large mountain ranges form