1. Topic: Plate Tectonics PSSA: 3.5.7.A / S8.D.1.1

2. Objective: TLW describe the three different types of tectonic plate boundaries. TLW explain how tectonic plates move.

3. MI #1: What is Plate Tectonics? Plate tectonics is the theory that the Earth’s lithosphere is divided into large plates that move on top of the asthenosphere. It helps explain how mountains form. It also explains what causes most earthquakes and volcanos.

4. MI #2: Convergent Boundaries A plate boundary is where two tectonic plates touch. Convergent boundaries are where two tectonic plates collide. There are three possible types of convergent boundaries…continental- continental, continental–oceanic, and oceanic-oceanic.

5. MI #3: What happens at convergent boundaries? Continental-continental: the edges of the plates buckle and thicken, forming mountains. Continental-oceanic: this is a subduction zone, the denser oceanic plate sinks (or is subducted) into the asthenosphere. Oceanic-oceanic: the denser oceanic plate is subducted.

6. MI #4: Divergent Boundaries A divergent boundary is where two tectonic plates are moving apart; this usually happens at a mid-ocean ridge. Divergent boundaries are where new sea floor is being formed.

7. MI #5: Transform Boundaries A transform boundary is where two tectonic plates are sliding horizontally past each other. The San Andreas Fault in California is a good example.

8. MI #6: What causes plate motion? Ridge push – At mid-ocean ridges the new ocean floor is higher then the older ocean floor, so it slides downhill, pushing the older floor away from the ridge. Convection – the rising and sinking of the asthenosphere due to it being hotter near the center of the Earth. Slab pull – Dense oceanic lithosphere is subducted and pulls the oceanic plate along.

9. So What…? Real Life Application Understanding plate tectonics is important because it is responsible for mountain building, earthquakes, volcanoes, and continental drift.