18: Chapter Geologic Time
Multiple Choice
1. In 1869, ____________, who was later to head the U.S. Geological Survey, led a pioneering expedition down the Colorado River and through the Grand Canyon. a. James Ussher b. John Wesley Powell c. William Smith
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d. John Playfair e. James Hutton 2. Approximately how old is Earth currently thought to be? a. 4 to 5 million years b. 6000 years c. 40 billion years d. 90 million e. none of the above
3. The subdivisions of the geologic time scale that represent the greatest expanse of time are called ____________. a. epoch b. era c. period d. stage e. none of the above
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4. Which one of the following represents the greatest expanse of time? a. Mesozoic b. Cenozoic c. Precambrian d. Paleozoic 5. By applying the law of superposition, ____________ dates can be determined. a. numerical
b. c. d. e.
radiometric relative isotope both numerical and radiometric
6. The era of "ancient life" is the _________ era. a. Cenozoic
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b. c. d. e.
Precambrian Neolithic Mesozoic none of the above
c. d. e.
Neolithic Mesozoic none of the above
7. The era of "recent life" is the _________ era. a. Cenozoic b. Precambrian
8. About 85 percent of geologic time is represented by the time span called the ____________. a. Paleozoic b. Stone Age c. Precambrian
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d. e.
Cretaceous Ordovician
e.
none of the above
9. When a beta particle is emitted during radioactive decay ____________. a. the atomic number remains the same b. the atomic number decreases by 1 c. the atomic number increases by 1 d. the mass number drops by 1 and the atomic number remains unchanged
10. If a radioactive isotope (atomic number 90, mass number 232) emits 6 alpha particles and 4 beta particles during the course of radioactive decay, what is the atomic number and mass number of the stable daughter product? a. atomic number 100, mass number 256
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b. c. d. e.
atomic number 82, mass number 208 atomic number 98, mass number 222 atomic number 74, mass number 208 none of the above
Geologic Time
11. If the half-life of a material x is 1000 years and you found a specimen with equal amounts of material x and material z (the daughter product) the specimen would be about ____________. a. 500 years old b. 1000 years old c. 1500 years old d. 2000 years old
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e.
it is not possible to determine from the information given
e.
3 billion
12. Abundant fossil evidence did not appear in the geologic record until about _________ years ago. a. 5 billion b. 6 million c. 600 million d. 300 million
13. Of 5 undeformed horizontal beds of sedimentary rock, we can say that _________. a. the top layer is oldest b. the lowest layer is oldest c. the third layer from the bottom is older than the second layer from the bottom
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d.
there is no way of knowing which layer is oldest
14. An unconformity is a(n) ____________. a. layer of sedimentary rock b. gap in the rock record c. layer of rock with very unusual fossils d. intrusion e. none of the above
15. Fossils, which denote particular short periods of time in the geologic past, are referred to as ____________. a. environmental indicators b. fossil discriminators c. Huttonian fossils d. index fossils e. none of the above
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c. d. e. 16. In order to match rocks of similar age in different regions, geologists often use ____________. a. fossils b. sequence of beds
similarity of rock type all of the above only fossils and sequence of beds
17. Which of the following lists places the divisions of geologic time in order from longest to shortest? a. era, period, epoch b. epoch, period, era c. period, epoch, era
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d. e.
epoch, era, period none of the above
18. Groups of fossil plants and animals succeed each other in a definite and determinable order, and any period of time can be recognized by its respective fossils. The preceding is a statement of the _________. a. law of superposition
b. c. d. e.
concept of cross-cutting relationships principle of numerical dating law of original horizontality none of the above
19. Approximately what fraction of geologic time is represented by recorded history? a. 1/10 b. 1/100 c. 1/1000 d. 1/1,000,000
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e.
none of the above
e.
the atomic number decreases by 1 and the mass number increases by 1
20. One type of radioactive decay involves the capture of an electron by a nucleus. When this occurs ____________. a. the atomic number increases by 1 b. the atomic number decreases by 1 c. the mass number increases by 1 d. both the atomic number and the mass number increase by 1
21. With which type of radioactive decay does the atomic number remain unchanged?
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a. b. c. d. e.
alpha particle emission beta particle emission electron capture both beta particle emission and electron capture none of the above
c. d. e. 23.
two protons and two neutrons either two electrons and two neutrons or two protons and two neutrons none of the above
22. An alpha particle consists of _________. a. one electron b. two electrons and two neutrons
When an alpha particle is emitted, how, if at all, do the mass number and atomic number change? a. mass number 4 less, atomic number 2 less
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b. c. d. e.
mass number 2 less, atomic number 2 less mass number 4 less, atomic number unchanged mass number 4 less, atomic number 2 higher none of the above
24. During which type of radioactive decay does the mass number remain unchanged? a. alpha particle emission b. beta particle emission c. electron capture d. both alpha particle emission and beta particle emission e. both beta particle emission and electron capture
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25. When potassium_40 decays to argon_40, it does so by ____________. a. beta particle emission b. electron capture c. alpha particle emission d. both beta particle emission and electron capture e. both electron capture and alpha particle emission
Testban k
26. When uranium-238 decays to lead-206, it does so by ____________. a. electron capture b. beta particle emission c. alpha particle emission
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d. e.
both electron capture and beta particle emission both beta particle emission and alpha particle emission
b. c. d. e.
two three four none of the above
27. When three-quarters of a radioactive isotope has decayed to become the stable daughter product, ____________ halflives have occurred. a. one
28. When the ratio of radioactive parent to stable daughter product reaches 1:15, ____________ half-lives have passed. a. two b. four
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c. d. e.
eight fourteen fifteen
29. Assume that the half-life of a particular radioactive isotope is 10,000 years. Laboratory analysis shows that the ratio of radioactive parent to stable daughter product in a sample is 1:7. What is the age of the sample?
a. b. c. d. e.
1428.6 years 10,000 years 20,000 years 70,000 years none of the above
30. Radiocarbon is ____________. a. carbon-12 b. carbon-13 c. carbon-14
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d. e.
both carbon-13 and carbon-14 none of the above
31. Radiocarbon decays by which one of these processes?
b. c. d. e.
electron capture alpha particle emission neutron emission proton capture
Geologic Time
a. beta particle emission
32. The percentage of radioactive atoms that decay during one half-life ____________. a. is always the same b. continually decreases
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c. d. e.
continually increases depends upon the particular isotope in question none of the above
d. e.
all of the above both inclusions and superposition
33. Which of the following is related to relative dating? a. cross-cutting b. inclusions c. superposition
34. When tilted or folded sedimentary rocks are overlain by more flat-lying strata, a(n) ____________ is present. a. disconformity b. angular unconformity c. nonconformity d. conformity
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e.
none of the above
d.
35. A layer of sandstone is in contact with a mass of granite. The granite contains small pieces of the sandstone. Which rock is older? a. sandstone b. granite c. both are the same age
it is not possible to determine which is older from the information provided.
36. Which relative dating principle is illustrated in the previous question? a. cross-cutting b. original horizontality c. inclusions d. superposition
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e.
the described situation in the previous question does not illustrate any of these principles
37. An undeformed sedimentary layer is _____ than the layer above and _____ than the layer below. a. older, younger b. younger, older c. younger, younger d. older, older
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38. Which one of the following is credited with formulating the law of superposition? a. Nicolaus Steno b. William Smith c. John W. Powell d. Lord Kelvin e. James Hutton
39. The person most often credited with formulating the principle of faunal succession is ____________. a. Nicolaus Steno b. William Smith c. John W. Powell d. Lord Kelvin e. James Hutton
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40. Assume that you have just examined several flat-lying sedimentary layers. After much study you determine that there is a considerable span of time for which no sedimentary rock layer exists at this site. You have just discovered a(n) _________. a. angular unconformity b. series of conformable strata c. disconformity
d. e.
example of cross-cutting relation none of the above
41. A worm would stand a poor chance of being fossilized because ____________. a. worms have been rare during the geologic past b. worms have no hard parts c. worms contain no carbon_14
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a. b. c. d. d. e. all of the above none of the above
horse fish butterfly ant
Testban k
42. Which one of the organisms listed below would have the best chance of becoming part of the fossil record?
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43. Insects are sometimes preserved in the hardened resin of ancient trees. This material is called ____________. a. caprolite b. amber
c. d. e.
gastrolith carbonization none of the above
True-False:
44. The geologic time scale was originally constructed by scientists without the aid of numerical dates.
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45. We are now living in the Mesozoic era. 46. The Precambrian accounts for slightly less than one half of all geologic time. 47. Probably the single most characteristic feature of the Precambrian is its great abundance of fossil evidence. 48. The law of superposition is used in relative dating. 49. The era of "middle life" was the Mesozoic era.
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50. Of the Paleozoic, Mesozoic, and Cenozoic, the Mesozoic represents the greatest expanse of time. 51. Carbon_14 may be used to date events as far back as one million years. 52. Most samples of sedimentary rock can be accurately dated using radiometric techniques. 53. After two half-lives there is no longer any of the original radioactive material remaining. 54. An unconformity in which the strata are essentially parallel on either side is termed a disconformity.
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55. Unlike other commonly used radioactive isotopes, carbon_14 may be used to date organic materials. 56. Fossils are of little value in correlation. 57. When a beta particle is emitted, the mass number of the isotope remains unchanged. 58. Potassium has three natural isotopes, two of which are radioactive. 59. Potassium_40 decays to argon_40 by the emission of a beta particle.
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60. The percentage of radioactive atoms that decay during one half-life is always the same.
Geologic Time
61. The number of atoms in a radioactive sample that decay with each successive half-life continually decreases.
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62. Of the isotopes most frequently used for radiometric dating, uranium_238 has the shortest half-life. 63. An unconformity involving older metamorphic rocks and younger sedimentary strata is termed a nonconformity. 64. In reference to the geologic time scale, epochs are divided into smaller time units called periods. 65. The Paleozoic is the era of "ancient life."
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66. The Precambrian may also be referred to as the Phanerozoic eon. 67. It is usually not possible to obtain an accurate radiometric date from a sample of detrital sedimentary rock. 68. Epochs are subdivisions of periods. 69. All of geologic time prior to the beginning of the Paleozoic era is referred to as the Phanerozoic eon. 70. The oldest fossils date from the beginning of the Paleozoic era.
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Completion:
71. ____________ dating occurs when events are placed in their proper sequence or order without knowing their numerical ages. 72. The law of superposition is a principle used in _____________ dating. 73. The remains or traces of prehistoric life are called ____________.
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74. The principle of ____________ states that fossil organisms succeed one another in a definite and determinable order and that any time period can be recognized by its fossil content. 75. A(n) ____________ unconformity consists of tilted or folded rocks that are overlain by younger, more flat-lying strata. 76. We now live in the ____________ era. 77. The span of time prior to the beginning of the Mesozoic era is termed the ____________ era.
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78. List three common types of radioactive decay. ____________, ____________, ____________ 79. The time required for one half of the nuclei in a sample of a radioactive isotope to decay is called the ____________. 80. The stable daughter product that results from the decay of uranium_238 is ____________.
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Testban k
81. Carbon_14 is also called ____________. 82. "This dike is 10 million years old." The preceding statement is an example of a(n) ________ date. 83. "This sandstone layer is younger than these shale and limestone beds." The preceding statement is an example of _____________ dating.
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84. "In an undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below." The preceding is a statement of the law of ____________. 85. When one rock mass contains fragments of an adjacent rock mass, we know the adjacent rock mass must be older. The fragments used for relative dating in this situation are known as ____________. 86. Layers of sedimentary rock are said to be ____________ when they are found to have been deposited without interruption.
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87. List three different types of unconformities. ____________, ____________, ____________ 88. Disconformity and nonconformity are two different kinds of ____________. 89. An unconformity in which the strata on either side are essentially parallel is referred to as a(n) ____________. 90. An unconformity in which tilted or folded strata are overlain by more flat-laying layers is known as a(n) _____________ unconformity.
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91. The process of matching rocks of similar age in different regions is called ____________. 92. The era of "ancient life" is the ____________ era. 93. The era of "middle life" is the ____________ era. 94. The era of "recent life" is the ____________ era. 95. Each era is divided into smaller time units known as ____________, which in turn may be divided into still smaller units called ____________.
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96. All of geologic time prior to the beginning of the Paleozoic era is commonly referred to as the ____________. 97. The study of fossils and ancient life is called ____________. 98. Sometimes insects have been preserved in the hardened resin of ancient trees. This material is called ____________.
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Geologic Time
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Answers to Chapter 18 Test Questions
Multiple Choice: 1. 2. 3. 4. 5. b e e c c 11. 12. 13. 14. 15. b c b b d 21. 22. 23. 24. 25. e c a e b 31. 32. 33. 34. 35. a a d b a 41. b 42. b 43. b
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6. 7. 8. 9. 10.
e a c c b
16. 17. 18. 19. 20.
d a e d b
26. 27. 28. 29. 30.
e b b e c
36. 37. 38. 39. 40.
c a a b c
True- False: 44. true 45. false 46. false 52. false 53. false 54. true 60. true 61. true 62. false 68. true 69. false 70. false
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47. 48. 49. 50. 51.
false true true false false
55. 56. 57. 58. 59.
true false true false false
63. 64. 65. 66. 67.
true false true false true
Completion: 71. Relative 72. relative 85. inclusions 86 conformable
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73. 74. 75. 76. 77. 78.
fossils faunal succession angular Cenozoic Paleozoic alpha particle emission beta particle emission electron capture 79. half-life 80. lead_206
87. disconformity nonconformity angular unconformity 88. unconformities 89. disconformity 90. angular 91. correlation 92. Paleozoic 93. Mesozoic 94. Cenozoic
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81. radiocarbon 82. numerical
83. relative
95. periods, epochs 96. Precambrian 97. paleontology
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