Plate Tectonics

Theory of Continental Drift The theory that continents drifted across the ocean to get their current spots on the globe. First suggested by Alfred Wegner First used the idea of one super giant continent called Pangaea.

What was the evidence behind Wegner’s idea? The continents fit together like puzzle pieces. The fossils and rocks on separate continents being identical. Climate regions (found by looking at fossils) that did not match up with the positions the continents are located today.

Theory of Seafloor Spreading Molten material rises at the Mid-Ocean Ridge. The material flows away from the ridge, carrying the land that was once together, further apart.

Theory of PLATE TECTONICS First accepted in 1968 by a man named Hess. Combined the ideas of seafloor spreading and continental drift. States that the Earth’s crust and upper mantle are broken into sections called plates. Animation

Why do the plates move? Hot magma from within the Earth rises to the surface then cools down and sinks back into the Earth. (convection)

Convection Currents This is what powers the movement of the continents Graphic

What makes the plates move? 1.New seafloor is created and spreads out. 2. The continents on either side begin to move away from each other.

What makes the plates move? 3. Dense seafloor hits continental land. 4. Denser floor goes into the mantle and melts.

How do the plates move? The plates move in three different ways: Collide Separate Slide past each other

Convergent Plates Continent vs. Ocean The more dense ocean plate slides under the less dense continental plate (Subduction) Chains of volcanoes are formed along the edge of continents. Also trenches are formed off the coast of the continent. The Cascade Mountain chain is formed this way.

Convergent Plates Convergent Plates Ocean vs. Ocean Both dense plates are pushed towards the center of the Earth Extremely deep trenches are formed, and also chains of volcanic islands are created (island arcs) The Japanese Islands are formed this way.

Convergent Plates Continent vs. Continent When two continental plates hit both plates are forced up. No subduction occurs. Mountains are formed, not volcanoes. The Himalayan Mountains in India are formed this way.

Transform Boundary When one plate slides past another. The most famous is the San Andreas fault in California. No creation of anything, just destruction.

Divergent Boundary When two plates separate from each other. The Mid-Atlantic ridge is the best example. This is what caused Europe and the United States to separate. Animation