1. 1 The Theory of Plate Tectonics Earth’s Interior and Surface Plate Movements n Chapter 13 – n Time for Change The guy who started it all: Alfred Lothar Wegener 1880-1930

2. 2 Learning Targets n I will summarize the theory of plate tectonics. n I will identify and describe the three types of plate boundaries. n I will list and describe three causes of plate movement.

3. 1960’s Evidence supporting continental drift and sea- floor spreading lead to the development of a theory called plate tectonics, the theory that explains why and how continents move.

4. How Continents Move Earth’s crust and the rigid, upper part of the mantle form a layer called….. Earth’s crust and the rigid, upper part of the mantle form a layer called…..

5. The Lithosphere The thin outer shell that is broken into blocks, called tectonic plates, that ride on top of……. The thin outer shell that is broken into blocks, called tectonic plates, that ride on top of…….

6. The Asthenosphere A layer of solid rock that acts like a plastic, it flows like Sillyputty when put under pressure. A layer of solid rock that acts like a plastic, it flows like Sillyputty when put under pressure.

7. Two Types of Crust Oceanic: Thin, dense, high in iron (Fe) and magnesium (Mg). Continental: Thicker, less dense, high in silica (SiO 2 ). Tectonic plates can consist of only one type, or both.

8. Tectonic Plates  About 15 currently known.  While some can be identified by features easy to see (mountain ranges or ocean trenches), some cannot be.  We can identify plate boundaries by…….

9. Earthquakes  When plates move, they produce earthquakes, so we can say that 2 or more plates meet in that area.

10. Volcanoes Plate motions can form magma that erupts on the Earth’s surface as lava.

11. 11 Best Example n The “Pacific Ring of Fire”, an active zone of both volcanoes and earthquakes, indicating plate boundaries.

12. Types of Plate Boundaries Three main types, each associated with a characteristic type of geologic activity.

13. Divergent Boundaries Magma rising to the surface forces plates to move apart. Since the newly formed rock is warmer and lighter it sits higher than the surrounding rock. This forms the……. Magma rising to the surface forces plates to move apart. Since the newly formed rock is warmer and lighter it sits higher than the surrounding rock. This forms the…….

14. Mid-Ocean Ridges The undersea mountain ranges where new oceanic lithosphere is created. Down the center of the ridge is a rift valley, a narrow valley formed where the plates separate. The undersea mountain ranges where new oceanic lithosphere is created. Down the center of the ridge is a rift valley, a narrow valley formed where the plates separate.

15. Thingvellir fissure The rift valley (in shadow), the on- land exposure of the Mid-Atlantic Ridge in Iceland.

16. Can Occur On Continental Plates The East African Rift system is where Africa is currently breaking up, and has already formed the Red Sea by the separation of the African and Arabian plates. The East African Rift system is where Africa is currently breaking up, and has already formed the Red Sea by the separation of the African and Arabian plates.

17. Convergent Boundaries Formed where two plates collide. Three types of collisions can happen.

18. Oceanic to Continental Collision  Because oceanic lithosphere is denser, it subducts, or sinks below the continental plate. The area is called a subduction zone.

19. Deep Ocean Trenches  These form at subduction zones. The oceanic plate is heated and releases fluids into the overlying mantle, causing magma formation, which rises to the surface to form volcanoes.

20. Continent to Continent Collision Neither plate subducts, rather the edges crumple and thicken, causing the formation of large mountain ranges.

21. 21 Oceanic to Oceanic Collisions n One subducts under the other. Again, a trench is formed and magma rises to the surface to form an island arc, a chain of volcanic islands.

22. Transform Boundaries Where two plates slide past each other horizontally. They do not slide smoothly, producing earthquakes.

23. Also Occur at Mid-Ocean Ridges These short segments are called fracture zones and occur because spreading on a sphere cannot be a straight line.