Lesson 3 Reading Guide - KC

1. The Theory of Plate Tectonics • What is the theory of plate tectonics? • What are the three types of plate boundaries? • Why do tectonic plates move? Lesson 3 Reading Guide - KC

2. The Theory of Plate Tectonics • plate tectonics • lithosphere • divergent plate boundary • transform plate boundary • convergent plate boundary Lesson 3 Reading Guide - Vocab

3. The Theory of Plate Tectonics • subduction • convection • ridge push • slab pull Lesson 3 Reading Guide - Vocab

4. The Plate Tectonics Theory • The theory of plate tectonics, proposed in the late 1960s, states that Earth’s surface is made of rigid slabs of rock, or plates, that move with respect to each other. • Plate tectonics suggests that Earth’s surface is divided into large plates of rigid rock and each plate moves over Earth’s hot and semiplastic mantle. Lesson 3-1

5. The Plate Tectonics Theory(cont.) What is plate tectonics? Lesson 3-1

6. The Plate Tectonics Theory(cont.) • Geologists use the word tectonic to describe the forces that shape Earth’s surface and the rock structures that form as a result. • The cold and rigid outermost rock layer of the Earth is called the lithosphere. • The lithosphere is made up of the crust and the solid, uppermost mantle. Lesson 3-1

7. Earth’s Tectonic Plates Lesson 3-1

8. The Plate Tectonics Theory(cont.) • The lithosphere is thin below mid-ocean ridges and thick below continents. • Earth’s tectonic plates are large pieces of the lithosphere that fit together like the pieces of a giant jigsaw puzzle. • The layer of Earth below the lithosphere, called the asthenosphere, is so hot that it behaves like a plastic material and enables Earth’s plates to move. Lesson 3-1

9. The Plate Tectonics Theory(cont.) plastic Science Use capable of being molded or changing shape without breaking Common Use any of numerous organic, synthetic, or processed materials made into objects Lesson 3-2

10. Plate Boundaries • A divergent plate boundary forms where two plates separate. • When the seafloor spreads at a mid-ocean ridge, lava erupts, cools, and forms new oceanic crust. • Divergent plate boundaries can also exist in the middle of a continent, where they pull continents apart and form rift valleys. Lesson 3-2

11. Lesson 3-3

12. Plate Boundaries(cont.) • A transform plate boundary forms where two plates slide past each other. • As they move past one another, the plates can get stuck and stop moving. • Stress builds up where the plates are stuck until they eventually break and suddenly move apart, resulting in a rapid release of energy as earthquakes. Lesson 3-2

13. Lesson 3-3

14. Plate Boundaries(cont.) • Convergent plate boundaries form where two plates collide. • The denser plate sinks below the more buoyant plate in a process called subduction. • The area where a denser plate descends into Earth along a convergent plate boundary is called a subduction zone. Lesson 3-2

15. Plate Boundaries(cont.) subduction from Latin subductus, means “to lead under, removal” Lesson 3-2

16. Plate Boundaries(cont.) • When an oceanic plate and a continental plate collide, the denser oceanic plate subducts under the edge of the continent, creating a deep ocean trench and a line of volcanoes above the subducting plate on the edge of the continent. • When two continental plates collide, neither plate is subducted, and mountains form from uplifted rock. Lesson 3-2

17. Lesson 3-3

18. Lesson 3-3

19. Plate Boundaries(cont.) What are the three types of plate boundaries? Lesson 3-2

20. Evidence for Plate Tectonics • Scientists can measure how fast continents move using a network of satellites called the Global Positioning System. • Because plates are rigid, tectonic activity occurs where plates meet. Lesson 3-3

21. Evidence for Plate Tectonics(cont.) • Volcanoes form where plates separate along a mid-ocean ridge or continental rift or collide along a subduction zone. • Mountains can form where two continents collide. Lesson 3-3

22. Notice the relationship between earthquake epicenters, volcanoes, and plate boundaries. Lesson 3-3

23. Evidence for Plate Tectonics(cont.) How are earthquakes and volcanoes related to the theory of plate tectonics? Lesson 3-3

24. Plate Motion • Earth’s plates move because the asthenosphere moves underneath the lithosphere. • Convection is the circulation of material caused by differences in density. • Hot mantle material rises upward and comes in contact with Earth’s crust. Lesson 3-4

25. Plate Motion(cont.) • As the mantle cools, it becomes denser and then sinks, forming a convection current. • Convection currents in the asthenosphere act like a conveyor belt moving the lithosphere above it. • There are three forces that interact to cause plate motion: basal drag, ridge push, and slab pull. Lesson 3-4

26. Plate Motion(cont.) What causes convection? Lesson 3-4

27. Plate Motion(cont.) • Basal drag refers to how convection currents in the asthenosphere circulate and drag the lithosphere like a conveyor belt. • Rising mantle material at mid-ocean ridges creates the potential for plates to move away from the ridge with a force called ridge push. Lesson 3-4

28. As a slab, or dense plate, sinks, it pulls on the rest of the plate with a force called slab pull. Lesson 3-4

29. A Theory in Progress • Plate tectonics has become the unifying theory of geology, but several unanswered questions remain. • Why is Earth the only planet in the solar system that has plate tectonic activity? • Why do some earthquakes and volcanoes occur far away from plate boundaries? Lesson 3-5

30. What forces dominate plate motion? • What will scientists study next? This is a 3-D image of seismic wave velocities from a new technique called anisotropy. Lesson 3-5

31. Tectonic plates are made of cold and rigid slabs of rock. • Mantle convection—the circulation of mantle material due to density differences—drives plate motion. Lesson 3 - VS

32. The three types of plate boundaries are divergent, convergent, and transform boundaries. Lesson 3 - VS

33. What word do geologists use to describe the forces that shape Earth’s surface? A.semiplastic B. lithosphere C. tectonic D. mantle Lesson 3 – LR1

34. Which of these is made up of the crust and the solid, uppermost mantle? A. seafloor B. lithosphere C. biosphere D.hydrosphere Lesson 3 – LR2

35. What type of boundary forms where two plates separate? A.convergent plate boundary B.transform plate boundary C.new plate boundary D.divergent plate boundary Lesson 3 – LR3

36. Do you agree or disagree? 5. Continents drift across a molten mantle. 6. Mountain ranges can form when continents collide. Lesson 3 - Now