1. What we know…  Wegener collected evidence and proposed the theory of Continental Drift.  Hess found the “mechanism” to support the idea with his theory of Sea-Floor Spreading.

2. Put the two together… we get the Theory of Plate Tectonics.

3. Plate Tectonics  The Earth’s crust and rigid upper mantle are broken into huge slabs called tectonic plates (about a dozen major plates, and several smaller ones).

4.  Tectonic plates interact at places called plate boundaries.  This is where MOST of the action is really taking place.

5. Divergent Boundaries  The place where two tectonic plates are pulling away from each other (not always, but usually occurs on the seafloor).  A common feature associated with a divergent boundary is a ridge/rift.  A good example of a divergent boundary is the Mid- Atlantic Ridge.

6. Another Picture of a Divergent Boundary – A Mid-Ocean Ridge

7. Arguably the best example of a divergent boundary – The Mid-Atlantic Ridge

8. Convergent Boundaries  : The place where two tectonic plates are pushing against each other. –Oceanic/Continental: Basalt/Granite (a trench and a continental arc are formed) –Oceanic/Oceanic: Basalt/Basalt (a trench and an island arc are formed) –Continental/Continental: Granite/Granite (folded mountains are formed)

9. Convergent Boundaries Cont…  A common feature associated with a convergent boundary is a subduction.  A good example of a convergent boundary is the Mariana Trench / Mariana Island.

10. Transform Boundaries  The place where two tectonic plates are sliding past one another.  A good example of a transform boundary is the San Andres Fault in California.

11. More Photos of the San Andreas Fault

12. The San Andreas near San Francisco

13. … in Central California