Preview

1. Plate Tectonics Chapter 6 Preview Section 1 Earth's Structure Section 2The Theory of Plate Tectonics Section 3Deforming Earth's Crust Section 4California Geology Concept Map

2. Section 1 Earth's Structure Chapter 6 Bellringer Many fossils of the same ancient plants and animals are found on different continents separated by oceans. Write a few sentences to explain how this could happen and what it suggests about the continents. Write your answers in your science journal.

3. Section 1 Earth's Structure Chapter 6 What You Will Learn • Earth’s interior can be divided into layers based on chemical composition and physical properties. • Scientists use seismic waves to study Earth’s interior. • Continents are drifting apart from each other now and have done so in the past.

4. Section 1 Earth's Structure Chapter 6 The Layers of the Earth • Earth is made of several layers. • The materials in each layer have distinct properties. • Earth’s layers can be described in terms of their 1. chemical composition or 2. physical properties.

5. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued The Compositional Layers of Earth • Earth is divided into three compositional layers. • At Earth’s center, the dense metallic core is made mainly of the metal iron. • The dense, thick middle layer is the mantle.

6. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued • The mantle is made up largely of silicon, oxygen, and magnesium. • The surface layer, or crust, is composed mostly of silicon, oxygen, and aluminum.

7. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued

8. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued Continental and Oceanic Crust • There are two types of crust. • Continental crust is thicker than oceanic crust. • Both types are made mainly of the elements oxygen, silicon, and aluminum.

9. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued • But oceanic crust has almost twice as much iron, calcium, and magnesium as continental crust does. • These three elements form minerals that are denser than the minerals in continental crust. • These dense minerals make the thin oceanic crust heavier than the thicker continental crust.

10. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued The Physical Structure of Earth • Earth is divided into five layers based on physical properties. • These layers include: the lithosphere, the asthenosphere, the mesosphere, the inner core, and the outer core.

11. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued • The lithosphere is divided into pieces called tectonic plates and is rigid. • Below the lithosphere is the asthenosphere, which is a layer of the mantle that is made of very slow-flowing solid rock (magma). • Tectonic plates move on top of the asthenosphere.

12. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued • Below the asthenosphere is the mesosphere, which is the lower part of the mantle. • The mesosphere flows even more slowly than the asthenosphere. • Earth’s core has two layers.

13. Section 1 Earth's Structure Chapter 6 The Layers of the Earth, continued • The outer core is a layer of liquid iron and nickel. • At Earth’s center is the solid inner core. This layer is made mostly of nickel and iron. • The inner core is very hot, but it is solid because it is under enormous pressure.

14. Section 1 Earth's Structure Chapter 6 Mapping Earth’s Interior • Scientists have learned about Earth’s interior by studying earthquakes. • An earthquake produces vibrations called seismic waves. • Seismic waves travel through Earth at various speeds.

15. Section 1 Earth's Structure Chapter 6 Mapping Earth’s Interior, continued • Machines called seismometers measure the time seismic waves take to travel various distances from an earthquake’s center. • Scientists use these distances and times to calculate the density and thickness of Earth’s layers.

16. Section 1 Earth's Structure Chapter 6 Mapping Earth’s Interior, continued • The speed of seismic waves is affected by the type of material that the waves are traveling through. • For example, some types of waves can travel through rock but not through liquids.

17. Section 1 Earth's Structure Chapter 6 Mapping Earth’s Interior, continued • Scientists have found that such waves do not reach seismometers on the side of Earth opposite the earthquake. • So, part of Earth’s interior must be liquid. • This liquid layer is the outer core.

18. Section 1 Earth's Structure Chapter 6 Mapping Earth’s Interior, continued

19. Section 1 Earth's Structure Chapter 6 Continental Drift • Continental drift is the idea that a single large landmass broke up into smaller landmasses to form the continents, which then drifted to their present locations. • This idea explains how the continents seem to fit together.

20. Section 1 Earth's Structure Chapter 6 Continental Drift, continued • Continental drift also explains why fossils of the same plant and animal species are found on continents that are far away from each other. • Many of these ancient species could not have crossed an ocean.

21. Section 1 Earth's Structure Chapter 6 Continental Drift, continued • The locations of mountain ranges and similar types of rock also support continental drift.

22. Section 1 Earth's Structure Chapter 6 Continental Drift, continued • Scientists have used rock and fossil evidence to reconstruct past patterns of climate regions. • The distribution of these ancient climatic zones supports the idea of continental drift, too.

23. Section 1 Earth's Structure Chapter 6 The Breakup of Pangaea • Alfred Wegener, the scientist who proposed the theory of continental drift, proposed that the large continent of Pangaea gave rise to today’s continents. • Scientists have determined that Pangaea existed about 245 million years ago.

24. Section 1 Earth's Structure Chapter 6 The Breakup of Pangaea, continued • Pangaea split into two continents—Laurasia and Gondwana—about 135 million years ago. • These two continents then split into the continents we know today. • These continents slowly (centimeters per year) drifted to their present positions.

25. Section 1 Earth's Structure Chapter 6 The Breakup of Pangaea, continued

26. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading • Evidence for continental drift lies on the sea floor. • A chain of submerged mountains runs through the center of the Atlantic Ocean. • This mountain chain is part of a worldwide system of mid-ocean ridges.

27. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading, continued • Mid-ocean ridges show patterns of magnetism. • The pattern on one side of a ridge is the mirror image of the pattern on the other. • The magnetism of rocks aligns with Earth’s magnetic field as it was when the rocks formed.

28. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading, continued

29. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading, continued • Throughout Earth’s history, the north and south magnetic poles have changed place many times. • The process by which the poles change places is called magnetic reversal. • As rock forms from magma, minerals that contain iron form.

30. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading, continued • Some of the minerals in the new rocks being formed are magnetic and act like compasses. • They form so that their magnetic fields align with the magnetic fields on Earth.

31. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading, continued • When the molten rock cools, these tiny compasses are locked into position in the rock. • After Earth’s magnetic field reverses, new magnetic minerals that align in the opposite direction form.

32. Plate Tectonics Chapter 6 Magnetic Reversals and Sea-Floor Spreading

33. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading, continued • At a mid-ocean ridge, magma rises through fractures in the sea floor. • As magma cools, it forms new rock. • As the new rock forms, the older rock gets pulled away from the mid-ocean ridge.

34. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading, continued • The process by which new sea floor forms as old sea floor is pulled away is called sea-floor spreading. • The record of magnetic reversals on the sea floor provides evidence that the continents are moving. • Sea-floor spreading is one process that moves continents.

35. Section 1 Earth's Structure Chapter 6 Sea-Floor Spreading, continued

36. Section 2 The Theory of Plate Tectonics Chapter 6 Bellringer When water is heated in a pot over a flame, the flame touches only the bottom of the pot. How does the water become heated? Why does all of the air in a room become warm even if heat enters the room only through one furnace vent? Write your answers in your science journal.

37. Section 2 The Theory of Plate Tectonics Chapter 6 What You Will Learn • Earth’s lithosphere is broken into pieces called tectonic plates. • Heat from Earth’s interior causes convection in the mantle. • Tectonic plates move at an average rate of a few centimeters per year.

38. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plates • Plate tectonics is the theory that Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere. • Pieces of the lithosphere that move around on top of the asthenosphere are called tectonic plates.

39. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plates, continued • Earth’s tectonic plates differ in size. • Some plates contain both continental and oceanic crust. • Others contain mostly oceanic crust, or mostly continental crust.

40. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plates, continued

41. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plates, continued

42. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plates, continued • Tectonic plates float on the asthenosphere. • The plates cover the surface of the asthenosphere, and they touch one another and move around. • Thick plates made of continental lithosphere displace more asthenosphere than do thin plates made of oceanic lithosphere.

43. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plate Boundaries • A boundary is a place where tectonic plates meet. • Tectonic plate boundaries are located by studying the locations of earthquakes, volcanoes, and landforms such as mid-ocean ridges and ocean trenches. • A plate boundary can be a convergent, divergent, or transform boundary. (tectonic dance)

44. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plate Boundaries, continued

45. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plate Boundaries, continued Convergent Boundaries • The boundary at which two tectonic plates collide is a convergent boundary. • At a convergent boundary, three types of collisions may happen. • Continental/Continental: Two plates made of continental lithosphere collide, forming a high mountain range.

46. Notes continued… • An example of this type of collision is when the Indian Plate collides with the Eurasian Plate to make the Himalayan Mountain Range (Mt. Everest).

47. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plate Boundaries, continued • Continental/Oceanic: A plate of oceanic lithosphere collides with a plate of continental lithosphere. • The denser oceanic lithosphere will sink beneath the less-dense continental crust, in a process called subduction. • Subduction can cause a chain of volcanoes to form parallel to the plate boundary.

48. Notes continued… • One example of this type of collision is in the northwest where the Juan De Fuca plate is subducting under the North American Plate. (pg. 210-211) • Another example is the Pacific Plate subducting under the Eurasian plate to form Japan.

49. Section 2 The Theory of Plate Tectonics Chapter 6 Tectonic Plate Boundaries, continued • Oceanic/Oceanic: Two plates of oceanic lithosphere collide. • The denser of the two plates will subduct. • A series of volcanic islands, called an island arc, may form parallel to the plate boundary.

50. An example of land formed at this type of boundary are the Indonesian Islands.