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Answer Key Chapter 7, Section 2: pages 198-201 Directed Reading A: Restless Continents Section: Restless Continents WEGENER’S CONTINENTAL DRIFT HYPOTHESIS D ___ 1. What hypothesis by Alfred Wegener explains why continents seem to fit together? a. continental spreading c. Wegener’s puzzle b. plate tectonics d. continental drift A ___ 2. According to Wegener, how many landmasses did all continents once form? a. one c. seven b. six d. ten C ___ 3. What did Wegener hypothesize happened to the continents? a. They broke up and re-formed. b. They drifted together to form a single continent. c. They broke up and drifted to their current locations. d. They sank into the ocean. 4. Does fossil evidence support Wegener’s theory? Explain your answer. Wegener used fossils of the mesosaurus, a swimming reptile, and the glossopteris, a fern, found on different sides of the Atlantic Ocean. 5. List three kinds of evidence found on both sides of the ocean that support Wegener’s theory. Similar fossils – on different continents Similar rocks – same age and structure on different continents Glacier tracks – found on different continents going in the same direction Same ancient climatic conditions found on several continents THE BREAKUP OF PANGAEA 6. Wegener thought that all of the present continents were once joined 245 million years ago in a landmass he called Pangaea. 7. The single landmass split into two huge continents he called Gondwana and Laurasia about 180 million years ago. 8. When those two continents split 65 million years ago, what were formed? The present continents we see today in their present locations Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 4 Plate Tectonics Directed Reading A continued SEA-FLOOR SPREADING 9. Why did many scientists reject Wegener’s hypothesis? Scientist did not believe Wegener’s theory because he could not explain how and why the continents moved. 10. In the process of sea-floor spreading, what happens when magma rises to Earth’s surface and solidifies? Sea-floor spreading is the process of adding new oceanic lithosphere (crust) at a mid-ocean ridge (mountain chain on the ocean floor). Match the correct definition with the correct term. Write the letter in the space provided. C ____ 11. process of forming new oceanic lithosphere as magma rises to the surface B ___ 12. areas where sea-floor spreading takes place a. b. c. d. continental drift mid-ocean ridges sea-floor spreading magnetic reversal D ___ 13. process that happens when Earth’s magnetic poles change place A ___ 14. theory that explains how continents reached their current locations 15. Rock on the ocean floor provided the final proof of sea-floor spreading with a record of magnetic reversal. Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor. Holt Science and Technology 5 Plate Tectonics