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 • Earth’s continents had once been joined as a single landmass - Continental Drift - 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 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 Normal Polarity Reversed Polarity a change in Earth’s magnetic field. a magnetic field that has the same orientation as Earth’s present field 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 Convergent - places where tectonic plates interact with one another. Convergent plates come together. Divergent plates move away from one another. Transform plates move horizontally past one another

Divergent Boundary

Divergent - Iceland Rift

Convergent Oceanic- Continental Boundary

Oceanic-Continental Cascade Range

Convergent Oceanic-oceanic Boundary

Convergent Continent-Continent Boundary

Continental-Continental Himalayas

Transform Boundary

Transform – San Andreas Fault

Know this drawing!