1. Plate tectonics Theory that describes the formation, movements, and interactions of Earth’s lithospheres' plates. *Copy the notes that are in RED.*

2. Early ideas… Continental drift In 1912, German scientist Alfred Wegener proposed the hypothesis of continental drift. ▫This suggested that the continents moved, or drifted over a period of time. Wegener used the following to support his hypothesis: ▫Similarities in continents shape ▫Fossil remains of Mesosaurus (a reptile) only on South America & Africa. ▫Rock formations found on both continents

3. Continental drift (continued) An objection to Wegener’s theory was how did the continents move apart. Wegener suggested that the continents might float on deeper, more fluid layers, but had no evidence During his lifetime, Wegener was not successful in supporting his theory.

4. Theory of Plate tectonics In the 1950’s and 1960’s discoveries about earthquakes, magnetism and the ocean floor added some support to Wegener’s theory. Suggest that the continents are embedded(?) in lithospheric plates. As the plates move, they carry the continents with them.

5. *Outline the plate boundaries in RED* Plate boundary

6. Theory of Plate tectonics (continued) Explains why earthquakes and volcanoes are likely to occur in particular locations These boundaries are places where two plates are pushing toward, pulling away, or sliding past each other. Strain builds up and when the strain becomes too great, fractures form and earthquakes occur.

7. Theory of Plate tectonics (continued) There is high volcanic activity at these boundaries due to the high heat flow allowing molten rock to move upward. Evidence to support theory: ▫Magnetism of ocean floor

8. Theory of plate tectonics (continued) Geologist study the igneous rock of the ocean floor. Geologist discovered that the magnetic field of the ocean floor has reversed over time. The magnetism of the ocean floor “mirrors” itself from the mid-ocean ridge.

9. Theory of plate tectonics (continued) A mid-ocean ridge is a long chain of volcanic mountains on the ocean floor with a deep central valley. *VOCABULARY WORD*

10. Theory of plate tectonics (continued) *NEW OCEAN FLOOR IS MADE AT THE MID- OCEAN RIDGE* Why is it that new ocean floor is made at mid- ocean ridges? Ocean floor magnetism activity*

11. *NOTECARD DEMO* Mid-ocean ridge Oldest Trench Where subduction occurs. “recycling” *Seafloor spreading*

12. Theory of plate tectonics (continued) Geologist determined that the ages of the rock at the center was the youngest and on either side of the mid-ocean ridge the rock was older. *The ocean floor is older the farther away from the mid-ocean ridge.*

13. So what causes plates to move? Three theories have been proposed: ▫Ridge push ▫Mantel Convection ▫Slab pull

14. So what causes plates to move? Mantel Convection: heat from Earth’s core is transferred through the mantle. As the heat moves to the molten layer the hotter parts rise pushing down the cooler portion until it is warmed. This continues and creates a circular motion.

15. So what causes plates to move? (continued) Ridge push: the heated molten magma rises at the mid-ocean ridge. It is extremely hot and heats the rocks surrounding it. As the asthenosphere and lithosphere are heated they expand and become elevated producing a slope. (Mountain) Gravity causes older, denser lithosphere (crust) to slide away from the ridge *THIS IS OCCURING AT THE MID-OCEAN RIDGE*

16. So what causes plates to move? (continued) Slab pull: when the subducting plate pulls on the other plate. Ex: a coat is on the table, you drop keys in the pocket. The weight of the keys pulls the jacket off the table.

17. Types of Plate boundaries Divergent Convergent Transform *YOU WILL NEED TO DRAW A SIMPLE DIAGRAM TO ILLUSTRATE EACH ACTION WHICH OCCURS* *VOCABULARY WORDS*

18. Types of Plate boundaries (continued) Divergent boundary is where two plates are moving apart. ▫Most divergent boundaries are located in the ocean floor and have rift valleys. ▫Rift valleys are deep valleys at the center of the mid-ocean ridge. ▫Rift=crack in the ocean floor

21. Types of Plate boundaries Converging boundary is a boundary where two plates are moving toward each other. ▫2 classifications – subduction/collision ▫Subduction boundary: the boundary where two plates have collided and one has been pulled beneath the other. ▫The plate which is subducted descends into the mantle and is melted and recycled. ▫*forms deep-sea trenches*

22. Types of Plate boundaries (continued) Dependent on the type of crust converging different landforms are created.

26. Types of plate boundaries (continued) Transform boundary: boundary between two plates that are sliding past each other. ▫Ex: The North American plate is moving southeast and the Pacific plate is moving northwest.