1. Plate Tectonics

2. Alfred Wegener Proposed the Theory of Continental Drift
Evidence to support his theory
Fossils of the same plants and animals on South America, Africa and Antarctica
Continents of South America and Africa fit together like a puzzle
Coal Beds in the Appalachian Mountains line up with Coal beds in Great Britain

3. Harry Hess Proposed the Theory of Sea-floor Spreading
In the middle of the oceans, magma rises and pushes the continents out away from the mid- ocean ridge
The scientific community questioned why the Earth’s diameter wasn’t getting larger?
What was driving the rising magma in one region?

4. Convection currents
During WWII, studies were done of the ocean floor to lay telegraph line to Europe so we could communicate with troops.
Studies were done to find oil, much of which was known to be in ocean beds
The first sonar was used to map the ocean floor and much was explained about the movement of the plates
Subduction zones were the explanation of the recycling of the plates

5. Divergent Boundaries Plates move apart Land Features: Mid-Ocean Ridges
Shallow earthquakes
Magnetic striping
Newest crust on Earth
Rift Valley
Crater Volcanoes
Mid-Atlantic Ridge
Iceland
East African Rift Valley

6. Transform Boundaries Plates slip past each other Land features:
Fault lines
Frequent earthquakes
Shallow earthquakes
San Andreas Fault

7. Convergent Boundaries
Plates move toward each other
Oceanic plates are denser than continental plates
Denser plates sink below less dense plates – this is called subduction and subduction zones
Three types
Continental vs. continental
Continental vs. oceanic
Oceanic vs. oceanic

8. Convergent Boundaries
Continental vs Continental
plates push into each other and push up
Crust gets thicker
Neither plate subducts
Deep earthquakes
Himalayas are formed this way – they are still getting bigger

9. Convergent Boundaries
Continental vs Oceanic
Oceanic plate is denser and subducts
Where the plates meet they push each other down creating an ocean trench
Where the plate dives back into the mantle it melts and forces its way back to the surface creating a volcanic mountain range near the coast
Very deep earthquakes
Andes Mountains
Cascade Mountains

10. Convergent Boundaries
Oceanic vs Oceanic
One plate subducts – the older is denser
Crust material forces it’s way back to the surface and forms underwater volcanoes
Once they break the surface you get a volcanic island arc
Deepest ocean trenches
Mariana Trench
Japan
Aleutian Islands