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Plate Tectonics
Earth’s Interior
Alfred Wegener (1880-1930)
- German astronomer/meteorologist
- Died on expedition in 1930
- Proposed Continental Drift in 1912
Theory of Continental Drift
- Continental Drift
• Earth’s continents had
once been joined as a
single landmass
- Pangaea “all lands”
• Ancient landmass made up
of all continents forming a
supercontinent.
• Began to break apart about
200 million years ago (mya)
Pangaea Ultima?
Evidence from Rock
Formations
- Same rocks are found
in the Appalachians and
also in Greenland and
Europe.
- Rock formations (ex.
mountain ranges)
fractured as the
continents separated.
Evidence from Fossils
- Wegener found similar fossils of
different land animals and plants on
separated continents.
Paleaoclimatology
Evidence
- Sedimentary Rock Coal
• Coal forms from dead
swamp plants.
• Coal was found in
Antarctica, therefore
Antarctica must have been
closer to the equator at one
time.
Continental Drift was
rejected.
- Scientists rejected the
hypothesis because:
• People believed
continents and ocean
basins were fixed
features.
• Wegener could
not explain what forces
could cause a continent
to move.
Paleaoclimatology Evidence
- Glacial Deposits
• 290 mya glacial deposits found
in Africa, India, Australia, and
South America.
• These continents were once
located on the South Pole.
Theory of Plate Tectonics
Evidence.
- 1960s Technology:
• Magnetometer –makes a
map from detecting small
changes in magnetic fields.
• Geologists mapped
volcanoes and earthquakes
along plate boundaries.
• Sonar – used to map out
the seafloor (found mid-ocean
ridge).
Sea-Floor Spreading
Check this out on Google
EARTH.
Theory of Plate Tectonics
Evidence
1. Rock Age
•
•
•
Young Rocks –near ocean ridges.
Older Rocks –near deep-sea trenches
Seafloor Age – oldest part = 180 million years
old. Oldest Continental crust = 3.8 billion years
old.
Theory of Plate Tectonics
Evidence
2. Paleomagnetism is the past
formation of rocks containing iron and
show the direction of polarity of Earth’s
magnetic field. Ex. Basaltic rocks.
Magnetism & Paleomagnetism support sea-floor
spreading and Theory of Plate Tectonics.
Geomagnetic Time
Scale

Magnetic Reversal
a change in Earth’s magnetic field.

Normal Polarity
a magnetic field that has the same orientation as Earth’s
present field

Reversed Polarity
a magnetic field that is
opposite to the present field
Major plates of the world.
Mid-ocean Ridge – crust is
formed.
Subduction Zone – crust
is destroyed.
Slab-pull and Convection
Currents cause plate motion.
Plate Boundaries
Plate Boundaries
Three Major Types
1. Convergent
•plates come together.
2. Divergent
•plates move away from
one another.
3. Transform
•plates move horizontally
past one another
- places where tectonic plates
interact with one another.
Divergent Boundary
Divergent - Iceland Rift
Convergent OceanicContinental Boundary
Oceanic-Continental
Cascade Range
Convergent Oceanicoceanic Boundary
Convergent ContinentContinent Boundary
Continental-Continental
Himalayas
Transform Boundary
Transform – San Andreas
Fault
Know this drawing!