1. Plate Tectonics How the Earth moves

2. The Definition The theory of plate tectonics states that the Earth’s lithosphere is divided into pieces called tectonic plates that move around on top of the asthensophere Plates are either oceanic or continental

3. These plates drift very slowly— centimeters per year Once, the world had one giant supercontinent, called Pangea and one giant ocean. Then, over time, the supercontinent spread out, forming the 7 continents we know today—this process is described as continental drift

4. Sea-floor Spreading Magma rises from the mantle and solidifies—forming new oceanic lithosphere. Once the magma has solidified into the rocky crust, it spreads out in either direction

5. Divergent Boundary This is the boundary between two plates that are spreading away from one another –Like the ones found where sea-floor spreading occurs

6. Mid-Atlantic Ridge: A Divergent boundary

7. Convergent Boundary A convergent boundary is formed where two plates collide with each other Three combinations exist: –Continental/continental –Continental/oceanic –Oceanic/oceanic

8. The Three Collisions: Convergent Boundaries

9. Transform Boundaries A transform boundary can be found where two plates are sliding past each other horizontally –The most famous of which is the San Andreas Fault

10. The San Andreas Fault—A Transform Boundary

11. How Mountains Form

12. Types of Mountains— Folded Folded mountains form at convergent boundaries where plates collide Rock squeezes against rock, pushing it upward These form the highest mountains in the world

13. Types of Mountains— Fault-Block When the crust is tense, the rock can break along a series of faults, causing large rock blocks to drop down lower than other rocks

14. Types of Mountains— Volcanic Volcanic mountains form when oceanic crust sinks into the asthenosphere by subduction These rock melts, forming magma This magma, under pressure, eventually rises and erupts through volcanic mountains

15. The Ring of Fire