Chapter 18 Fossils and Geologic Time

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442 CHAPTER 18: FOSSILS AND GEOLOGIC TIME 14. What is the most useful technique a geologist can use to correlate the age of rock layers in widely separated outcrops of sedimentary rock? (1) compare the thickness of the rock layers (2) compare the fossils found in the rock layers (3) compare the grain sizes of the rock layers (4) compare the densities of minerals in the rock layers 15. The diagrams below are drawings of index fossils. Which pair can be found in Ordovician bedrock? and (1) and (2) Open-Ended Questions and (3) and (4) Base your answers to questions 16–18 on the following information and your knowledge of Earth science. Scientific evidence indicates that the earliest mammals probably evolved approximately 225 million years ago from an ancient reptile group called the therapsids. For millions of years afterward, early mammals and therapsids coexisted until the therapsids apparently became extinct 65 million years ago. However, geologists have recently found a fossil they believe to be a therapsid that is only 60 million years old. They found the fossil, which they have named Chronoperates paradoxus (paradoxical time wanderer) near Calgary in Canada. This find suggests that for 105 million years after the apparent extinction of the therapsids, a few of the reptiles continued to live in a narrow geographic range in Canada. 16. According to fossil evidence, during which geologic period did the earliest mammals appear on Earth?
CHAPTER REVIEW QUESTIONS 443 17. Explain briefly two reasons why Chronoperates paradoxus would not be a good index fossil. 18. State one method geologists could have used to determine that Chronoperates paradoxus lived 60 million years ago 19. Name one species of trilobites that might be found at Watertown, New York. 20. New York State has a natural record of most of its geologic history since the end of the Precambrian. Why are geologists unable to determine any New York State events from the Permian Period of the Paleozoic Era?
Page 1 and 2: DINOSAURS Chapter 18 Fossils and Ge
Page 3 and 4: ally the soft parts of an organism
Page 5 and 6: Figure 18-2 Footprint Puzzle WHAT A
Page 7 and 8: Rock fragments from Mars have been
Page 9 and 10: ACTIVITY 18-3 VARIATIONS WITHIN A S
Page 11 and 12: HOW HAS GEOLOGIC TIME BEEN DIVIDED?
Page 13 and 14: Figure 18-5 The wide geographic ran
Page 15 and 16: Figure 18-6 Changes in the number o
Page 17 and 18: First birds Extinction of dinosaurs
Page 19 and 20: 431
Page 21 and 22: HOW DO GEOLOGISTS CORRELATE ROCK LA
Page 23 and 24: Figure 18-9 Correlation. HOW DO GEO
Page 25 and 26: Figure 18-11 An exercise in correla
Page 27 and 28: (2) The length of each age depends
Page 29: 8. What is the geologic age of most

Chapter 18 Fossils and Geologic Time

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