Chapter 18 Fossils and Geologic Time

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438 CHAPTER 18: FOSSILS AND GEOLOGIC TIME TERMS TO KNOW thrown as high as 18,000 m into the atmosphere. While this is a major event in modern American history,Tambora, a volcano in Indonesia, ejected an estimated 30 cubic kilometers in 1815. Most of the debris from these explosions settled near the volcano. However, fine volcanic ash carried into the strong winds of the stratosphere can be deposited over a large area in a matter or days or weeks, a mere instant of geological time. If such a layer of ash is found in the rock strata over a broad area, it represents a very precise time marker that can be found in almost any environment of deposition. These precise time horizons can be very useful in the regional correlation of rock layers. Scientists also know that the impact of large asteroids, meteorites, or comets results in similar time markers. The impact event that marks the end of the Mesozoic Era was caused by an object estimated to be 10 km across. It created a crater more than 100 km in diameter on the Yucatan Peninsula of Mexico. An unknown quantity of rock from the crater and the remains of the flying object formed a dense cloud of dust. The dust was so widespread it blocked the sun and led to dramatic climatic changes over the whole planet. This event also deposited a distinctive layer of ash that can be found in sedimentary rocks on all the continents and in places on the floor of the ocean. This layer of ash very precisely marks the top boundary of rocks of Mesozoic age. correlation extinction paleontology evolution index fossil species CHAPTER REVIEW QUESTIONS 1. On what basis was the geologic time scale divided into eras and other divisions? (1) Earth’s history was divided into ages of time of equal length in millions of years.
(2) The length of each age depends on the half-life of a radioactive substance. (3) The evolutionary development of life-forms was used to divide geologic time. (4) Geologic time was based on motions of the moon and Earth. 2. What group of fossil organisms was alive during the Paleozoic Era, but did not live in any other time period? (1) dinosaurs (3) trilobites (2) brachiopods (4) corals 3. Nautiloids are a group of marine animals that have been alive for almost 500 million years. The form of nautiloid that paleontologists call Centroceras is known to have been abundant how long ago? (1) 500 million years ago (3) 300 million years ago (2) 400 million years ago (4) 200 million years ago 4. The diagram below is a portion of a geologic time line. Letters A, B, C, and D represent the time intervals between labeled events. A B C D Present Dinosaur extinction Earliest flowering plants Earliest dinosaur Extinction of trilobites Fossil evidence indicates that the earliest birds developed during which time period? (1) A (3) C (2) B (4) D 5. During which era did the initial opening of the present-day Atlantic Ocean most likely occur? (1) Cenozoic (3) Paleozoic (2) Mesozoic (4) Late Proterozoic CHAPTER REVIEW QUESTIONS 439
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
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Page 21 and 22: HOW DO GEOLOGISTS CORRELATE ROCK LA
Page 23 and 24: Figure 18-9 Correlation. HOW DO GEO
Page 25: Figure 18-11 An exercise in correla
Page 29 and 30: 8. What is the geologic age of most
Page 31: CHAPTER REVIEW QUESTIONS 443 17. Ex

Chapter 18 Fossils and Geologic Time

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