Radioactive Decay 1. Due to radioactive decay, an igneous rock sample now contains one-fourth of the amount of potassium-40 that it originally contained. The age, in years, of this rock sample is approximately A) 0.7 x 10 9 years C) 2.6 x 10 9 years B) 1.3 x 10 9 years D) 5.2 x 10 9 years 2. Which radioactive element is used to determine the absolute age of late Pleistocene animal remains? A) rubidium-87 C) potassium-40 B) uranium-238 D) carbon-14 3. How much of an 800-gram sample of potassium-40 will remain after 3.9 × 10 9 years of radioactive decay? A) 50 grams B) 100 grams C) 200 grams D) 400 grams 4. Base your answer to the following question on the passage below. Frozen Mammoth A wooly mammoth was found in 1999 buried in the frozen soil of the Siberian tundra. Carbon-14 dating indicated that it had died about 20,000 years ago. Many fossils represent only the partial remains of organisms. However, a complete mammoth with bones, skin, hair, and internal organs intact represented a unique opportunity for scientists to investigate the lifestyle of this animal and the environment in which it lived. Identify both the period and epoch of geologic time during which the wooly mammoth lived. Radioactive Decay 5. The table below shows how the radioactive decay of potassium-40 can be used to determine the age of a rock. How old is a sample of granite that contains 8 grams of radioactive potassium-40 and 56 grams of its nonradioactive decay products? A) 1.3 × 10 9 B) 2.6 × 10 9 C) 3.9 × 10 9 D) 5.2 × 10 9 6. The diagram below represents a sample of rubidium-87 ( 87 Rb). Which diagram represents the correct proportion of after two half-lives? A) B) C) 87 Rb D) to its decay product, 87 Sr, Radioactive Decay 7. The table below shows information about the radioactive decay of carbon-14. What is the amount of carbon-14 remaining after 28,500 years? A) g B) g C) g D) g Base your answers to questions 8 and 9 on the graph below, which shows the generalized rate of decay of radioactive isotopes over 5 half-lives. 8. Which radioactive isotope takes the greatest amount of time to undergo the change shown on the graph? A) carbon-14 C) uranium-238 B) potassium-40 D) rubidium-87 Radioactive Decay 9. If the original mass of a radioactive isotope was 24 grams, how many grams would remain after 3 half-lives? A) 12 B) 24 C) 3 D) 6 10. How old is a fossil that has radioactively decayed through 4 half-lives of carbon-14? A) 5,700 years C) 22,800 years B) 17,100 years D) 28,500 years 11. An igneous rock contains 10 grams of radioactive potassium-40 and a total of 10 grams of its decay products. During which geologic time interval was this rock most likely formed? A) Middle Archean C) Middle Proterozoic B) Late Archean D) Late Proterozoic Radioactive Decay 12. The diagram below represents a sample of a radioactive isotope. Which diagram best represents the percentage of this radioactive isotope sample that will remain after 2 half-lives? A) B) C) D) 13. A whalebone that originally contained 200 grams of radioactive carbon-14 now contains 25 grams of carbon-14. How many carbon-14 half-lives have passed since this whale was alive? A) 1 B) 2 C) 3 D) 4 Radioactive Decay 14. The graph below shows the radioactive decay of a 50-gram sample of a radioactive isotope. According to the graph, what is the half-life of this isotope? A) 100 years B) 150 years C) 200 years D) 300 years Radioactive Decay 15. The models below represent the decay of radioactive atoms to stable atoms after their first and second half-lives. Which model best represents the number of undecayed and decayed atoms after three half-lives? A) B) C) D) Radioactive Decay 16. The graph below shows the rate of decay of the radioactive isotope K-40 into the decay products Ar-40 and Ca-40. Analysis of a basalt rock sample shows that 25% of its radioactive K-40 remained undecayed. How old is the basalt? A) 1.3 billion years C) 3.9 billion years B) 2.6 billion years D) 4.6 billion years Base your answers to questions 17 and 18 on the diagram below, which represents a model of a radioactive sample with a half-life of 5000 years. The white boxes represent undecayed radioactive material and the shaded boxes represent the decayed material after the first half-life. 17. Which radioactive isotope has a half-life closest in duration to this radioactive sample? A) carbon-14 C) uranium-238 B) potassium-40 D) rubidium-87 Radioactive Decay 18. How many more boxes should be shaded to represent the additional decayed material formed during the second half-life? A) 12 B) 6 C) 3 D) 0 19. A fossil shell contains 25% of the original amount of its carbon-14. Approximately how many years ago was this shell part of a living organism? A) 5,700 years ago C) 17,100 years ago B) 11,400 years ago D) 22,800 years ago 20. Which graph best shows the radioactive decay of carbon-14? A) B) C) D) 21. A sample of wood that originally contained 100 grams of carbon-14 now contains only 25 grams of carbon-14. Approximately how many years ago was this sample part of a living tree? A) 2,850 years C) 11,400 years B) 5,700 years D) 17,100 years Radioactive Decay 22. Uranium-238 that crystallized at the same time Earth formed has undergone approximately how many half-lives of radioactive decay? A) one half-life C) three half-lives B) two half-lives D) four half-lives 23. Fossil pollen has been recovered from sediments deposited in late-Pleistocene lakes. The pollen’s geologic age can most accurately be measured by using A) rubidium-87 C) oxygen-18 B) potassium-40 D) carbon-14 24. The characteristic of the radioactive isotope uranium-238 that makes this isotope useful for accurately dating the age of a rock is the isotope’s A) B) C) D) organic origin constant half-life common occurrence in sediments resistance to weathering and erosion Radioactive Decay 25. The table below gives information about the radioactive decay of carbon-14. Part of the table has been deliberately left blank for student use. After how many years will A) 22,800 yr B) 28,500 yr gram of the original carbon-14 reamins? C) 34,200 yr D) 39,900 yr 26. A sample of wood found in an ancient tomb contains 25% of its original carbon-14. The age of this wood sample is approximately A) 2,800 years C) 11,400 years B) 5,700 years D) 17,100 years 27. A student filled a graduated cylinder with 1,000 milliliters of water to represent a radioactive substance. After 30 seconds, the student poured out one-half of the water in the cylinder to represent the decay occurring within the first half-life. The student repeated the process every 30 seconds. How much water did the student pour from the cylinder at the 2-minute mark? A) 12.5 mL B) 62.5 mL C) 125.0 mL D) 250.0 mL Radioactive Decay 28. The diagram below represents the present number of decayed and undecayed atoms in a sample that was originally 100% radioactive material. If the half-life of the radioactive material is 1,000 years, what is the age of the sample represented by the diagram? A) 1,000 yr B) 2,000 yr C) 3,000 yr D) 4,000 yr 29. Which radioactive isotope is most useful for determining the age of mastodont bones found in late Pleistocene sediments? A) uranium-238 C) potassium-40 B) carbon-14 D) rubidium-87 30. The absolute age of a rock is the approximate number of years ago that the rock formed. The absolute age of an igneous rock can best be determined by A) comparing the amounts of decayed and undecayed radioactive isotopes in the rock B) comparing the sizes of the crystals found in the upper and lower parts of the rock C) examining the rock's relative position in a rock outcrop D) examining the environment in which the rock is found 31. Carbon-14, an isotope used to date recent organic remains, would most likely be useful in determining the age of a fossil A) trilobite C) armored fish B) Coelophysis D) Beluga whale Radioactive Decay 32. Why are radioactive substances useful for measuring geologic time? A) The ratio of decay products to radioactive substances remains constant in rocks. B) The half-lives of radioactive substances are short. C) Samples of radioactive substances are easy to collect from rocks. D) Radioactive substances undergo decay at a predictable rate. 33. A bone sample contains only the bone sample? A) 1 C 14 half-life C) 9 C 14 half-lives of its original radioactive C 14 content. How old is B) 2 C 14 half-lives D) 4 C 14 half-lives Base your answers to questions 34 through 38 on the graph below, which represents the decay of radioactive material X into a stable decay product. 34. If radioactive material X were heated, the length of its half-life period would A) decrease C) remain the same B) increase Radioactive Decay 35. Each of the objects below has different amounts remaining of the original radioactive material X. Which object is most likely the oldest? A) B) C) D) 36. Which graph best represents the relative percentages of radioactive material X and its stable decay product after 15,000 years? (The shaded region represents radioactive material while the non-shaded region represents stable decay products.) A) B) C) D) 37. Radioactive material X can only be used to date young geologic material because radioactive material X A) B) C) D) has only recently become radioactive has a relatively short half-life never existed in older rocks has only recently been discovered Radioactive Decay 38. What is the approximate half-life of radioactive material X? A) 5,000 yr B) 10,000 yr C) 50,000 yr D) 100,000 yr 39. Which process could be indicated by the expression below? U 238 ® Pb 206 A) B) C) D) crystallization of minerals in basalt chemical weathering of marble radioactive decay in granite ozone depletion in the atmosphere 40. The half-life of a radioactive substance is mainly controlled by the A) B) C) D) amount of the substance composition of the substance pressure acting on the substance temperature of the substance 41. Samples of plant pollen are preserved in sediment deposited by the last glacial ice sheet. Which radioactive isotope is best for determining the age of the samples? A) potassium-40 C) uranium-238 B) carbon-14 D) rubidium-87 42. Which two elements are most useful for the radioactive dating of recent organic remains? A) C 14 and N 14 C) U 238 and Pb 206 B) K 40 and Ca 40 D) Rb 87 and Sr 87 Radioactive Decay 43. A graph of the radioactive decay of carbon-14 is shown below. Which graph correctly shows the accumulation of nitrogen-14, the decay product of carbon-14, over the same period? A) B) C) D) 44. If a sample of a radioactive substance is crushed the half-life of the substance will A) decrease C) remain the same B) increase Radioactive Decay 45. The table below gives information about the radioactive decay of carbon-14. [Part of the table has been left blank for student use.] What is the amount of the original carbon-14 remaining after 34,200 years? A) g B) g C) g D) g 46. An archeologist found an ancient skeleton estimated to be 10,000 to 25,000 years old. Which radioactive isotope would be most useful for finding the age of the skeleton? A) carbon-14 C) uranium-238 B) potassium-40 D) rubidium-87 47. What is the approximate age of an igneous rock that contains only one-fourth of its original potassium-40 content due to radioactive decay? A) 1.3 × 10 9 years C) 3.9 × 10 9 years B) 2.6 × 10 9 years D) 5.2 × 10 9 years Radioactive Decay 48. Base your answer to the following question on the map below, which shows an area of the northwestern United States affected by a major volcanic eruption at Crater Lake during the Holocene Epoch. The age of this volcanic eruption was most accurately determined to be Holocene by measuring the radioactive A) B) C) D) potassium in the fine-grained volcanic rock carbon in trees buried by the ash uranium in the volcanic ash rubidium in the igneous glass 49. An ancient bone was analyzed and found to contain carbon-14 that had decayed for nearly two half-lives. Approximately how old is the bone? A) 1,400 years C) 5,600 years B) 2,800 years D) 11,000 years Radioactive Decay 50. Which statement best explains why geologic materials from the Quarternary Period must be dated by using radioactive isotopes different from the isotopes used to date materials from the Cambrian Period? A) B) C) D) All rocks contain radioactive substances. Some isotopes decay faster than others. Not all isotopes form stable decay products. The decay of atoms occurs as a random event. 51. The diagram below represents the skull of a saber-toothed tiger that died 30,000 years ago. The age of the skull could be determined most accurately by using A) uranium-238 C) potassium-40 B) rubidium-87 D) carbon-14 52. If a sample of a radioactive substance is crushed, the half-life of the substance will A) decrease C) remain the same B) increase Radioactive Decay 53. The table below gives information about the radioactive decay of carbon-14. [Part of the table has been left blank for student use.] What is the amount of the original carbon-14 remaining after 34,200 years? A) 1/8 g B) 1/16 g C) 1/32 g D) 1/64 g 54. Using radioactive dating methods and mathematical inferences, scientists have estimated the date of Earth's formation to be approximately A) 1.1 × 10 6 years ago C) 3.3 × 10 9 years ago B) 2.4 × 10 6 years ago D) 4.6 × 10 9 years ago 55. Radioactive carbon-14 dating has determined that a fossil is 5.7 × 10 3 years old. What is the total amount of the original C l4 still present in the fossil? A) 0% B) 25% C) 50% D) 75% 56. A rock contains uranium-238, which has a half-life of 4.5 × 109 years. If the rock is crushed and heated, the half-life of the uranium-238 it contains will A) decrease C) remain the same B) increase Radioactive Decay 57. An igneous rock contains one-half of its original amount of potassium-40. The age of the igneous rock is closest to A) 0.7 × 10 9 years C) 2.1 × 10 9 years B) 1.4 × 10 9 years D) 2.8 × 10 9 years 58. Which radioactive element would be used to determine the age of late Pleistocene mastodont bones found in western Connecticut? A) carbon-14 C) uranium-238 B) potassium-40 D) rubidium-87 59. Which radioactive isotope disintegrates to lead (Pb 206)? A) C 14 B) K 40 C) Rb 87 D) U 238 Radioactive Decay 60. The diagram below represents the radioactive decay of uranium-238. Shaded areas on the diagram represent the amount of A) B) C) D) undecayed radioactive uranium-238 (U 238) undecayed radioactive rubidium-87 (Rb 87 ) stable carbon-14 (C 14 ) stable lead-206 (Pb 206) 61. A marine fossil was found to contain one-half of its original quantity of carbon-14. Approximately how old is this fossil? A) 5,700 years C) 17,100 years B) 11,400 years D) 22,800 years 62. Two rock units contain the same radioactive substance. Rock A is buried deep underground; rock B is at the Earth's surface. Which statement best describes the half-life of the radioactive substance? A) B) C) D) The radioactive substance in rock A has a longer half-life. The radioactive substance in rock B has a longer half-life. The radioactive substance has the same half-life in rock A and in rock B. The radioactive substance's half-life has increased with time in rocks A and B. Radioactive Decay Base your answers to questions 63 through 67 on the graph below which shows the decay rates of four radioactive substances, A, B, C, and D. 63. Decay rates of radioactive substances such as these can be used to determine the age of rocks and fossils because radioactive decay occurs A) B) C) D) at a steady, predictable rate in all types of sedimentary rock only when a living organism dies in all organic and mineral substances 64. The half-life of these radioactive substances depends on the A) pressure acting on the material B) amount of the material C) temperature of the material D) composition of the material 65. When 90 percent of the original mass of isotope D remains, what total percent of the original mass of isotope B remains? A) 10% B) 22% C) 63% D) 90% 66. The radioactive substance uranium-238 is represented by A) A B) B C) C D) D Radioactive Decay 67. Which radioactive substance has a half-life of 13 billion years? A) A B) B C) C D) D 68. Compared to the length of time for the first half-life of a sample of a radioactive isotope, the length of time for the second half-life is A) less B) greater C) the same 69. The age of a Moon rock can be found by analyzing a sample to compare the relative amounts of A) U 238 and Pb 206 C) C 14 and Pb 206 B) U 238 and C 14 D) U 238 and Sr 87 70. The half-life of uranium-238 is A) 4,500 years C) 4,500,000,000 years B) 4,500,000 years D) 45,000,000,000 years 71. Radioactive carbon (C l4 ) would be especially useful in determining the age of A) B) C) D) geologically young organic remains geologically young inorganic remains Precambrian igneous rocks extremely small amounts of material 72. Which element is used by Earth scientists for radioactive dating of rocks? A) cobalt-60 C) potassium-40 B) plutonium-244 D) silicon-28 Radioactive Decay 73. The decay rates of radioactive substances remain constant when the substances are subjected to different temperature and pressure conditions. The best inference that can be drawn from this statement is that decay rates are A) B) C) D) independent of external factors independent of the isotope's composition affected by the mass of the isotope affected by pressure, but not by temperature 74. The diagram below shows the relative proportions of carbon-14 (C-14) to nitrogen-14 (N-14) in a rock. What is the most likely age of the rock? A) 2.85 × 10 3 B) 5.7 × 10 3 C) 1.3 × 10 9 D) 4.5 × 10 9 75. Which radioactive element has a half-life of 4.5 × 10 9 years? A) carbon-14 C) uranium-238 B) rubidium-87 D) potassium-40 76. What are the respective decay products of uranium, potassium, and rubidium? A) B) C) D) lead (Pb), argon (Ar), and strontium (Sr) carbon (C), oxygen (O), and nitrogen (N) hydrogen (H), lithium (Li), and helium (He) silicon (Si), oxygen (O), and aluminum (Al) Radioactive Decay 77. One similarity between uranium-238 and carbon-14 is that both A) B) C) D) decay at a predictable rate have the same half-life are normally found in large quantities in living matter are found in granite 78. The diagram below represents a clock used to time the half-life of a particular radioactive substance. The clock was started at 12:00. The shaded portion on the clock represents the number of hours one-half of this radioactive substance took to disintegrate. Which diagram best represents the clock at the end of the next half-life of this radioactive substance? A) B) C) D) 79. Which radioactive element would be most useful for determining the age of clothing that is thought to have been worn 2,000 years ago? A) carbon-14 C) uranium-238 B) potassium-40 D) rubidium-87 Radioactive Decay Base your answers to questions 80 through 84 on the graph below which shows the rate of radioactive decay of element A and the rate at which decay product B is formed. 80. Two rocks containing radioactive element A were taken from a mine. One had a mass of 2 grams; the other had a mass of 4 grams. Compared to the half-life of element A in the 4-gram sample, the half-life of element A in the 2-gram sample will be A) shorter B) longer C) the same 81. If the radioactive element in a rock sample is potassium-40, which resulting decay product would be present? A) Sr 87 B) Ar 40 C) N 14 D) C 12 82. If the half-life of radioactive element A is 10,000 years, for which time interval would this element be most useful in determining the age of rock? A) Precambrian C) Mississippian B) Devonian D) Pleistocene Radioactive Decay 83. An igneous rock contains 2 grams of radioactive element A and 2 grams of decay product B. How old is the rock sample? A) 1 half-life C) 3 half-lives B) 2 half-lives D) less than 1 half-life 84. According to the graph, what is the total percentage of radioactive element A present after 3 half-lives? A) 12.5% B) 25.0% C) 75.0 % D) 87.5% 85. Which graph best represents the decay rate of potassium-40? A) B) C) D) 86. If a specimen of a given radioactive substance is reduced in size, its half-life will A) decrease C) remain the same B) increase 87. A geologist uses carbon-14 to determine the age of a sample of material found in a sedimentary deposit. If the sample shows that 50 percent of the original carbon-14 is left, what is the approximate age of the sample? A) 1,400 years C) 5,600 years B) 2,800 years D) 11,200 years Radioactive Decay 88. Radioactive elements can be used for dating rocks because the disintegration rate of radioactive elements A) B) C) D) is not affected by the environment is linked to the Earth's motions can be controlled by scientists can increase with time 89. Which graph best represents the relationship between the remaining mass of a radioactive element and time? A) B) C) D) 90. The graph below shows the relationship between mass and time for four radioactive elements during radioactive decay. Which line best represents the decay curve for potassium-40? A) A B) B C) C D) D Radioactive Decay 91. What is the half-life of carbon-14? A) 5.7 years C) 5,700 years B) 570 years D) 5,700,000 years 92. Which radioactive substance shown on the graph below has the longest half-life? A) A B) B C) C D) D 93. Radiocarbon dating shows that a fossil contains half of its original radioactive carbon-14. What is the approximate age of the fossil? A) 5,600 years C) 16,800 years B) 11,200 years D) 4,500,000 years Radioactive Decay 94. The graph below shows the percent remaining (not decayed) of the original amount of carbon-14 at different times (A, B, and C) during radioactive decay. How many half-lives of time are represented by point B along the time axis? A) 1 half-life B) 2 half-lives C) 3 half-lives D) 4 half-lives 95. Why are radioactive materials useful for measuring geologic time? A) The disintegration of radioactive materials occurs at a predictable rate. B) The half-lives of most radioactive materials are less than five minutes. C) The ratio of decay products to undecayed material remains constant in sedimentary rocks. D) Measurable samples of radioactive materials are easily collected from most rock types. Radioactive Decay 96. Base your answer on the diagram below which represents a cube of radioactive material (figure A) cut into eight identical cubes (figure B). Compared to the half-life of the material in figure A, the half-life of the material in each small cube in figure B is A) 1/8 as long C) 8 times longer B) 1/64 as long D) the same 97. Which radioactive substance would probably be used in dating the recent remains of a plant found in sedimentary deposits? A) carbon-14 C) rubidium-87 B) potassium-40 D) uranium-238 98. Which radioactive substance has the longest half-life? A) carbon-14 C) rubidium-87 B) potassium-40 D) uranium-238 99. One half of the radioactive potassium-40 (K 40 ) in an igneous rock has decayed to argon-40 (Ar 40 ). About how many years ago was this rock formed? A) 1.4 × 10 9 B) 2.8 × 10 9 C) 4.2 × 10 9 D) 9.8 × 10 9 Radioactive Decay 100. A rock sample containing the radioactive isotope potassium-40 is calculated to be 4.2 × 10 9 years old. How much of the original potassium-40 would be left in this rock sample? A) 0 B) 1/8 C) 1/4 D) 1/2 101. The element K 40 radioactively decays to Ar 40 . The diagram below shows a model of the relative amounts of K 40 and Ar 40 remaining after one half-life. Which diagram best illustrates the relative amounts of K 40 and Ar 40 remaining after two half-lives? A) B) C) D) 102. Which radioactive element would a scientist most likely have used to date the age of a fossil that is 10,000 years old? A) potassium-40 C) uranium-238 B) carbon-14 D) rubidium-87 103. A rock sample contained 8 grams of potassium-40 (K 40 ) when it was formed, but now contains only 4 grams due to radioactive decay. What is the approximate age of this rock? A) 0.7 × 10 9 years C) 2.8 × 10 9 years B) 1.4 × 10 9 years D) 5.6 × 10 9 years

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