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2. Resources Chapter Presentation Visual Concepts Transparencies Standardized Test Prep Brain Food Video Quiz

3. Chapter 10 Plate Tectonics Table of Contents Section 1 Continental Drift Section 2 The Theory of Plate Tectonics Section 3 The Changing Continents

4. Chapter 10 Section 1 Continental Drift Objectives • SummarizeWegener’s hypothesis of continental drift. • Describethe process of sea-floor spreading. • Identifyhow paleomagnetism provides support for the idea of sea-floor spreading. • Explainhow sea-floor spreading provides a mechanism for continental drift.

5. Chapter 10 Section 1 Continental Drift Wegener’s Hypothesis • Continental drift the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present location • The hypothesis of continental drift was first proposed by German scientist Alfred Wegener in 1912. • Wegener used several different types of evidence to support his hypothesis

6. Chapter 10 Section 1 Continental Drift Wegener’s Hypothesis, continued Wegener’s Evidence • Fossil Evidence: fossils of the same plants and animals could be found in areas of continents that had once been connected. • Evidence from Rock Formations: ages and types of rocks in the coastal regions of widely separated areas matched closely. • Climatic Evidence: changes in climatic patterns suggested the continents had not always been located where they are now.

7. Chapter 10 Section 1 Continental Drift Wegener’s Hypothesis, continued Similar rock formations and fossil evidence supported Wegener’s hypothesis.

8. Chapter 10 Section 1 Continental Drift Wegener’s Hypothesis, continued Missing Mechanisms • Wegener proposed that the continents moved by plowing through the rock of the ocean floor. • Wegener’s ideas were strongly opposed. • Wegener’s mechanism was disproved by geologic evidence. • Wegener spent the rest of his life searching for a mechanism for the movement of continents.

9. Chapter 10 Section 1 Continental Drift Wegener’s Hypothesis, continued Reading Check Why did many scientists reject Wegener’s hypothesis of continental drift?

10. Chapter 10 Section 1 Continental Drift Wegener’s Hypothesis, continued Reading Check Answer Why did many scientists reject Wegener’s hypothesis of continental drift? Many scientists rejected Wegener’s hypothesis because the mechanism that Wegener suggested was easily disproved by geologic evidence.

11. Chapter 10 Section 1 Continental Drift Mid-Ocean Ridges • Mid-ocean ridge a long, undersea mountain chain that has a steep, narrow valley at its center, that forms as magma rises from the asthenosphere, and that creates new oceanic lithosphere (sea floor) as tectonic plates move apart

12. Chapter 10 Section 1 Continental Drift Mid-Ocean Ridges, continued In 1947, a group of scientists set out to map the Mid-Atlantic Ridge. While studying the Mid-Atlantic Ridge, scientists noticed two surprising trends. • The sediment that covers the sea floor is thinner closer to a ridge than it is farther from the ridge • The ocean floor is very young. Rocks on land are as old as 3.8 billion years. None of the oceanic rocks are more than 175 million years old.

13. Chapter 10 Section 1 Continental Drift Mid-Ocean Ridges, continued Rocks closer to a mid-ocean ridge are younger than rocks farther from the ridge. Rocks closer to the ridge are covered with less sediment than rocks farther from the ridge.

14. Chapter 10 Section 1 Continental Drift Sea-Floor Spreading • Sea-floor spreading the process by which new oceanic lithosphere (sea floor) forms as magma rises to Earth’s surface and solidifies at a mid-ocean ridge • Paleomagnetism the study of the alignment of magnetic minerals in rock, specifically as it relates to the reversal of Earth’s magnetic poles; also the magnetic properties that rock acquires during formation

15. Chapter 10 Section 1 Continental Drift Sea-Floor Spreading, continued • In the late 1950’s geologist Harry Hess proposed that the valley at the center of the mid-ocean ridge was a crack, or rift, in Earth’s crust. • As the ocean floor moves away from the ridge, molten rock, or magma, rises to fill the crack. • Hess suggested that if the sea floor is moving, the continents might be moving also. • He suggested this might be the mechanism that Wegener was searching for.

16. Chapter 10 Section 1 Continental Drift Sea-Floor Spreading, continued As the ocean floor spreads apart, magma rises to fill the rift and then cools to form new rock.

17. Chapter 10 Section 1 Continental Drift Sea-Floor Spreading, continued

18. Chapter 10 Section 1 Continental Drift Sea-Floor Spreading, continued

19. Chapter 10 Section 1 Continental Drift Sea-Floor Spreading, continued Reading Check How does new sea floor form?

20. Chapter 10 Section 1 Continental Drift Sea-Floor Spreading, continued Reading Check Answer How does new sea floor form? New sea floor forms as magma rises to fill the rift that forms when the ocean floor moves away from a mid-ocean ridge.

21. Chapter 10 Section 1 Continental Drift Paleomagnetism • Paleomagnetism the study of the alignment of magnetic minerals in rock, specifically as it relates to the reversal of Earth’s magnetic poles; also the magnetic properties that rock acquires during formation As magma solidifies to form rock, iron-rich minerals in the magma align with Earth’s magnetic field. When the rock hardens, the magnetic orientation of the minerals becomes permanent.

22. Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Magnetic Reversals Scientists have discovered rocks whose magnetic orientations point opposite of Earth’s current magnetic field. • Rocks with magnetic fields that point north (normal polarity) are all classified in the same time periods. • Rocks with magnetic fields that point south (reversed polarity) also all fell into specific time periods

23. Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Magnetic Reversals When scientists placed these periods of normal and reversed polarity in chronological order, they discovered a pattern of alternating normal and reversed polarity in the rocks. Scientists used this pattern to create the geomagnetic reversal time scale.

24. Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Magnetic Symmetry Scientists discovered a striped magnetic pattern on the ocean floor on each side of a mid-ocean ridge. The pattern on one side of the ridge is a mirror image of the pattern on the other side. When drawn on a map, these patterns match the geomagnetic reversal time scale.

25. Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Magnetic Symmetry The pattern of magnetic symmetry and age of rock formation indicate that new rock forms at the center of a ridge and then move away from the center in opposite directions.

26. Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Reading Check How are magnetic patterns in sea-floor rock evidence of sea-floor spreading?

27. Chapter 10 Section 1 Continental Drift Paleomagnetism, continued Reading Check Answer How are magnetic patterns in sea-floor rock evidence of sea-floor spreading? The symmetrical magnetic patterns in sea-floor rocks show that rocks formed at one place (at a ridge) and then broke apart and moved away from the center in opposite directions.

28. Chapter 10 Section 1 Continental Drift Wegener Redeemed • Reversal patterns on the sea floor could also be found on land. The reversals in land rocks also matched the geomagnetic reversal time scale. • Because the same pattern appears in rocks of the same ages on both land and the sea floor, scientists agreed that the magnetic patterns showed change over time. • The idea of sea-floor spreading provides a way for the continents to move over the Earth’s surface. • Sea-floor spreading was the mechanism that verified Wegener’s hypothesis of continental drift.

29. Chapter 10 Section 1 Continental Drift Continental Drift (Pangaea)

30. Section 2 The Theory of Plate Tectonics Chapter 10 Objectives • Summarizethe theory of plate tectonics. • Identifyand describe the three types of plate boundaries. • Listand describe three causes of plate movement.

31. Section 2 The Theory of Plate Tectonics Chapter 10 How Continents Move • plate tectonics the theory that explains how large pieces of the lithospehere, called plates, move and change shape • lithosphere the solid, outer layer of Earth that consists of the crust and the rigid upper part of the mantle • asthenosphere the solid, plastic layer of the mantle beneath the lithosphere; made of mantle rock that flows very slowly, which allows tectonic plates to move on top of it

32. Section 2 The Theory of Plate Tectonics Chapter 10 How Continents Move, continued • The lithosphere forms the thinouter shell of Earth and isbroken into several blocks ortectonic plates. • The tectonic plates ride onthe asthenoshpere in much the same way that blocks of wood float on water. • Tectonic plates can include continental crust, oceanic crust, or both. • Continents and oceans are carried along on the moving tectonic plates in the same way that passengersare carried by a bus.

33. Section 2 The Theory of Plate Tectonics Chapter 10 Tectonic Plates • Scientists have identified about 15 major tectonic plates. • Scientists identify plate boundaries primarily by studying data from earthquakes. • The locations of volcanoes can also help identify the locations of plate boundaries.

34. Section 2 The Theory of Plate Tectonics Chapter 10 Tectonic Plates, continued The boundaries of tectonic plates do not always match the outlines of continents.

35. Section 2 The Theory of Plate Tectonics Chapter 10 Tectonic Plates, continued Reading Check How do scientists identify locations of plate boundaries?

36. Section 2 The Theory of Plate Tectonics Chapter 10 Tectonic Plates, continued Reading Check Answer How do scientists identify locations of plate boundaries? Scientists use the locations of earthquakes, volcanoes, trenches, and mid-ocean ridges to outline tectonic plates.

37. Section 2 The Theory of Plate Tectonics Chapter 10 Types of Plate Boundaries • Tectonic plate boundaries may be in the middle of the ocean floor, around the edges of continents, or even within continents. • The three types of plate boundaries are divergent boundaries, convergent boundaries, and transform boundaries. • Each plate boundary is associated with a characteristic type of geologic activity.

38. Section 2 The Theory of Plate Tectonics Chapter 10 Types of Plate Boundaries, continued • insert TT

39. Section 2 The Theory of Plate Tectonics Chapter 10 Types of Plate Boundaries, continued • insert TT

40. Section 2 The Theory of Plate Tectonics Chapter 10 Types of Plate Boundaries, continued • insert TT

41. Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion • Many scientists think that the movement of tectonic plates is partly due to convection. • Convection is the movement of heated material due to differences in density that are caused by differences in temperatures.

42. Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued • The convection process can be modeled by boiling water in a pot on the stove. As the water at the bottom of the pot is heated, the water at the bottom expands and becomes less dense than the cooler water above it. • The cooler, denser water sinks, and the warmer water rises to the surface to create a cycle called aconvection cell.

43. Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued Mantle Convection • Scientists think that tectonic plates are part of a convection system. • Energy generated by Earth’s core and radioactivity within the mantle heat the mantle. This heated material rises through the cooler, denser material around it.

44. Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued Mantle Convection • As the hot material rises, the cooler, denser material flows away from the hot material and sinks into the mantle to replace the rising material. • As the mantle material moves, it drags the overlying tectonic plates along with it.

45. Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued • Insert TT

46. Section 2 The Theory of Plate Tectonics Chapter 10 Causes of Plate Motion, continued • Insert TT

47. Section 2 The Theory of Plate Tectonics Chapter 10 Plate Tectonics

48. Section 3 The Changing Continents Chapter 10 Objectives • Identifyhow movements of tectonic plates change Earth’s surface. • Summarizehow movements of tectonic plates have influenced climates and life on Earth. • Describethe supercontinent cycle.

49. Section 3 The Changing Continents Chapter 10 Reshaping Earth’s Crust • rifting the process by which Earth’s crust breaks apart; can occur within continental crust or oceanic crust • Slow movements of tectonic plates change the size and shape of the continents over millions of years. • All of the continents that exist today contain large areas of stable rock, called cratons, that are older than 540 million years. Rocks within the cratons that have been exposed at Earth’s surface are called shields. • One way that continents change shape is by breaking apart. Rifting is the process by which a continent breaks apart.

50. Section 3 The Changing Continents Chapter 10 Reshaping Earth’s Crust, continued • terrane a piece of lithosphere that has a unique geologic history and that may be part of a larger piece of lithosphere, such as a continent • Continents change not only by breaking apart but also by gaining material. Most continents consist of cratons surrounded by a patchwork of terranes. • Terranes become part of a continent at convergent boundaries. When a tectonic plate carrying a terrane subducts under a plate made of continental lithosphere, the terrane is scraped off of the subducting plate and becomes part of the continent.