1. Plate Tectonics Plate Tectonics

2. A Little History....... 4.5 billion Our Planet is approximately 4.5 billion years old. PANGEA About 240 million years ago the continents were all one giant land mass. It was called PANGEA. Alfred Wegener The theory of Continental Drift was proposed in 1912 by Alfred Wegener. Plate Tectonics This theory was not generally accepted until the 1960’s, at which time it became called the science of Plate Tectonics.

3. Problems? he could not explain how the continents drifted apart Wegener’s theory was not accepted because he could not explain how the continents drifted apart. Arthur Holmes Arthur Holmes proposed that the Earth’s mantle was a hot, soupy layer that the continents slid around on.

4. Slip, Sliding Away...... boundarys The places where the earth’s cracks meet are called boundarys. TransformDivergentConvergent There are 3 types of boundarys: Transform, Divergent, and Convergent.

5. Types of Boundarys..... Divergentseparate move away sea floor spreading Divergent- plates separate and move away from each other- sea floor spreading.

6. Convergent Convergent- plates move towards each other. This is how mountain ranges are formed. Subduction Subduction occurs when the heavier (more dense) plate moves under the lighter (less dense) plate.

7. Transform sliding in opposite directions Transform- this occurs when plates are sliding in opposite directions next to each other (most earthquakes occur at these boundarys). The San Andreas Fault in California is an example of a Transform Boundary.