Directed Reading. Section: The Theory of Plate Tectonics. to the development of plate tectonics, developed? HOW CONTINENTS MOVE

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1 Skills Worksheet Directed Reading Section: The Theory of Plate Tectonics 1. The theory that explains why and how continents move is called. 2. By what time period was evidence supporting continental drift, which led to the development of plate tectonics, developed? HOW CONTINENTS MOVE In the space provided, write the letter of the definition that best matches the term or phrase. 3. oceanic crust 4. continental crust 5. tectonic plates 6. lithosphere 7. asthenosphere a. the solid outer layer of Earth, that consists of the crust and the rigid upper part of the mantle b. dense crust made of rock that is rich in iron and magnesium c. blocks of Earth s shell that ride on a deformable layer of the mantle d. solid, plastic layer of the mantle beneath the lithosphere e. low-density crust made of rock that is rich in silica 8. What is plastic rock and how does it move? 9. Describe how continents and oceans are carried on tectonic plates. TECTONIC PLATES 10. How many major tectonic plates have scientists identified? 11. Why are the boundaries of the tectonic plates not always easy to identify? Holt Earth Science 13 Plate Tectonics

2 12. How do scientists identify plate boundaries? 13. A sudden movement along the boundary of a tectonic plate is a(n). 14. Frequent earthquakes in a given zone are evidence that 15. How do volcanoes help identify the locations of plates boundaries? 16. A zone of active volcanoes that encircles the Pacific Ocean is known as the. 17. In addition to volcanoes, what also occurs frequently in the Pacific Ring of Fire? 18. What do the characteristics of the Pacific Ring of Fire indicate? TYPES OF PLATE BOUNDARIES In the space provided, write the letter of the definition that best matches the term or phrase. 19. divergent 20. convergent 21. transform 22. mid-ocean ridge 23. subduction zone 24. fracture zone a. boundary between tectonic plates that are sliding past each other horizontally b. region where one plate moves under another c. boundary between tectonic plates that are moving away from each other d. undersea mountain range e. short segments of a mid-ocean ridge that are connected by transform boundaries f. the boundary between tectonic plates that are colliding Holt Earth Science 14 Plate Tectonics

3 25. Name three areas where plate boundaries may be located. 26. What happens to magma at divergent boundaries? 27. Describe the rock that forms when magma cools to form new oceanic lithosphere. 28. A narrow area that forms where the plates at a divergent boundary separate is called a. 29. Where are most divergent boundaries located? 30. Describe an example of a rift valley. 31. When oceanic lithosphere collides with continental lithosphere, the oceanic lithosphere is less dense than the continental lithosphere, so it sinks, or. 32. What deep-ocean feature forms at subduction zones? 33. As the oceanic plate subducts, it releases fluids into the mantle, causing magma to form and rise to the surface, forming. Holt Earth Science 15 Plate Tectonics

4 34. What happens when two plates made of continental lithosphere collide? 35. What is an example of a large mountain range formed when two plates made of continental lithosphere collided? 36. What happens when two plates made of oceanic lithosphere collide? 37. What is produced from magma formed from melted mantle rock? 38. An example of a feature that formed when two plates made of oceanic lithosphere collided is. 39. What causes earthquakes at transform boundaries? 40. How are transform boundaries different from other types of boundaries? 41. An example of a transform boundary is the. 42. The San Andreas Fault is located between what two plates? 43. Transform boundaries that connect short segments of a mid-ocean ridge are called. 44. What is an example of a convergent boundary? 45. What is an example of a divergent boundary in the mid-atlantic? Holt Earth Science 16 Plate Tectonics

5 CAUSES OF PLATE MOTION 46. The movement of heated material due to differences in density is called a. convection. b. a convection cell. c. radioactivity. d. plate motion. 47. The cycle in which the cooler, denser water sinks and the warmer water rises to the surface to create a cycle is called a. convection. b. plate tectonics. c. a convection cell. d. boiling water. 48. Earth s mantle is heated by a. tectonic plates. b. core energy and radioactivity. c. boiling water. d. cool, dense mantle material. 49. What causes tectonic plate movement? a. Hot material in the mantle sinks. b. Lack of a convection cell causes plates to rise. c. The mantle drags overlying tectonic plates along. d. Divergent boundaries come together. 50. What happens to newer, warmer rock at a mid-ocean ridge as it cools? a. It is elevated above nearby rock. b. It slopes downward away from the ridge. c. It sinks into the mantle and pulls away from the ridge. d. It exerts force on the plate. 51. The force on the rest of the plate from the asthenosphere below cooling, sinking rock is called. 52. What happens as a result of ridge push? Holt Earth Science 17 Plate Tectonics

6 53. Is ridge push the main driving force of plate motion? Along with ridge push, what did scientists study for clues to forces that drive plate motion? 54. What happens to magma in places where plates pull away from each other at mid-ocean ridges? 55. The force exerted by a sinking plate caused by the subduction of lithosphere into the asthenosphere is called. 56. Compared to speed of plates that are not subducting, plates that are subducting move. 57. What three forces work together to cause plate motions? Holt Earth Science 18 Plate Tectonics

7 ANSWER KEY 7. A 8. If the continents had once been joined, fossils of the same plants and animals should be found in areas that were once connected. 9. in South America and western Africa 10. because it was unlikely that the reptiles had swum across the Atlantic and there was no evidence that land bridges had once connected the continents 11. Although the areas where the rocks came from were widely separated, the ages and types of rocks matched closely. 12. Mountain chains that ended at the coastline of one continent seemed to continue on other continents across the ocean. 13. The Appalachians extend northward along the east coast of North America; mountains of similar age and structure are found in Greenland, Scotland, and northern Europe. 14. that the continents have not always been located where they are now 15. fossil evidence, such as plant fossils 16. If the continents were once joined and positioned differently, there would have been climate differences. 17. He thought the continents plowed through the rock of the ocean floor. 18. Wegener s theory was easily disproved by geologic evidence. 19. He died before he identified a plausible mechanism for the movement of continents. 20. C 21. B 22. D 23. B 24. B 25. D 26. C 27. A 28. Magma rises from a rift in the ocean floor and fills it. As the ocean floor moves away, the magma cools and solidifies to form new rock that replaces the ocean floor. 29. Earth has north and south geomagnetic poles. 30. The compass needle aligns with the field of magnetic force that extends from one of Earth s poles to the other. 31. As magma turns to rock, iron-rich minerals align with Earth s magnetic field. The magnetic orientation becomes permanent when the rock hardens. 32. Scientists have discovered rocks whose magnetic orientations point opposite to Earth s current magnetic field. 33. normal polarity 34. reversed polarity 35. alternating normal and reversed polarity 36. geomagnetic reversal time scale 37. The striped magnetic pattern on one side of a mid-ocean ridge is a mirror image of the striped pattern on the other side of the ridge. 38. alternating bands of normal and reversed polarity matching the geomagnetic reversal time scale 39. As new sea floor forms, it records reversals in Earth s magnetic field. 40. They matched the magnetic patterns on each side of a mid-ocean ridge to the geomagnetic reversal time scale. 41. at the center of the ridge 42. farther away on either side of the ridge 43. at the rift in a mid-ocean ridge 44. New rock forms at the center of a ridge and then moves away from the center in opposite directions. 45. The symmetry of magnetic patterns and the symmetry of ages of sea-floor rocks 46. C 47. D 48. D SECTION: THE THEORY OF PLATE TECTONICS 1. plate tectonics 2. by the 1960s 3. B 4. E 5. C 6. A 7. D 8. solid rock under great pressure that flows slowly, like putty Holt Earth Science 54 Plate Tectonics

8 ANSWER KEY 9. in the same way that passengers are carried by a bus They don t always match the familiar outlines of continents and oceans. 12. by studying data from earthquakes 13. earthquake 14. that two or more plates may meet in the area 15. Some volcanoes form when plate motions generate magma that erupts on Earth s surface. 16. Pacific Ring of Fire 17. earthquakes 18. that the Pacific Ocean is surrounded by plate boundaries 19. C 20. F 21. A 22. D 23. B 24. E 25. in the middle of the ocean floor, around the edges of continents, and within continents 26. Magma rises to the surface as plates move apart. 27. warm and light 28. rift valley 29. on the ocean floor 30. the Red Sea, between the African and Arabian plates 31. subducts 32. deep-ocean trench 33. volcanic mountains 34. The colliding edges crumple and thicken, forming large mountain ranges. 35. the Himalalya Mountains 36. One plate subducts under the other, forming a deep-ocean trench. Fluids from the subducted plate cause mantle rock to melt and form magma. 37. a chain of volcanic islands called an island arc 38. Japan 39. As plates slide past each other horizontally, they scrape against each other. 40. They do not produce magma. 41. San Andreas Fault 42. North American and Pacific plates 43. fracture zones 44. the Chilean trench along the west coast of South America 45. the boundary of the North American and Eurasian plates 46. A 47. C 48. B 49. C 50. C 51. ridge push 52. It pushes the rest of the plate away from the mid-ocean ridge. 53. convergent boundaries 54. It rises to the surface. 55. slab pull 56. faster 57. drag on the bottoms of tectonic plates, ridge push, and slab pull SECTION: THE CHANGING CONTINENTS 1. They change the size and shape of the continents over millions of years. 2. A 3. C 4. B 5. It is thick with a high silica content. 6. heat from the mantle building up beneath the continent 7. A rift forms in the zone of weakness and the continent begins to break apart. 8. by breaking apart and by gaining material 9. C 10. B 11. A 12. D 13. They are different from those of neighboring terranes. 14. major faults 15. They generally do not match those of neighboring terranes. 16. The terrane is scraped off the subducting plate. 17. They might become mountains or simply add to the surface area of the continent. 18. seamounts, atolls, or large chunks of continental crust 19. Major mountain chains often form. 20. Himalaya Mountains 21. its location in relation to the equator and the poles, its location in relation Holt Earth Science 55 Plate Tectonics