1. Plate Tectonics

2. Sea-Floor Spreading
Process by which new oceanic lithosphere is created as older materials are pulled away
Creates Mid-Ocean Ridges
Underwater Mountain Chains

3. Theory of Plate Tectonics
Theory that both continental and oceanic crust move
Theory states:
Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere

4. Causes of Motion Heat and Gravity Convection Slab Pull
Hot material rises and cooler material sinks. Drags tectonic plates sideways
Slab Pull
Oceanic lithosphere is denser than the asthenosphere.
Oceanic plate sinks and pulls
the rest of the plate with it

5. Tectonic Plate Boundaries
Convergent
Two plates push into another
Result depends on what type of crust
Continental / continental
Push crust upward
Continental / Oceanic
Oceanic plate slides under
Oceanic / Oceanic
One of the plates slides
under

7. Tectonic Plate Boundaries
Divergent
Two plates move away from each other
Examples:
Sea-floor spreading
Mid-ocean ridges are the most common
Can be found on continents

8. Sea-Floor Spreading Process
Plates move away from each other
Creates a gap in the sea floor
Magma rises to fill gap
Magma cools and forms underwater mountains

9. Newer Crust = At the Mid-ocean crust
Older Crust = Edges of continents

10. Tectonic Plate Boundaries
Transform
Two plates slide past each other horizontally
Plates are smooth so they grind and jerk
Cause Earthquakes
Example
San Andreas Fault in California

13. Tracking Plate Motion Slow and Gradual
Measured in centimeters per year
Measure using GPS
Global Positioning System