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A. A solidified lava flow containing zircon mineral crystals is present in a sequence of rock layers that are exposed in a hillside. A mass spectrometer analysis was used to count the atoms of uranium-235 and lead-207 isotopes in zircon samples from the lava flow. The analysis revealed that 71% of the atoms were uranium-235, and 29% of the atoms were lead-207. Refer to Figure 8.10 to help you answer the following questions. 1. About how many half-lives of the uranium-235 to lead-207 decay pair have elapsed in the zircon crystals? 2. What is the absolute age of the lava flow based on its zircon crystals? Show your calculations. 3. What is the age of the rock layers beneath the lava flow? 4. What is the age of the rock layers above the lava flow?

A. A solidified lava flow containing zircon mineral crystals is present in a sequence of rock layers that are exposed in a hillside. A mass spectrometer analysis was used to count the atoms of uranium-235 and lead-207 isotopes in zircon samples from the lava flow. The analysis revealed that 71% of the atoms were uranium-235, and 29% of the atoms were lead-207. Refer to Figure 8.10 to help you answer the following questions. 1. About how many half-lives of the uranium-235 to lead-207 decay pair have elapsed in the zircon crystals? 2. What is the absolute age of the lava flow based on its zircon crystals? Show your calculations. 3. What is the age of the rock layers beneath the lava flow? 4. What is the age of the rock layers above the lava flow?

Applications and Investigations in Earth Science (9th Edition)
Applications and Investigations in Earth Science (9th Edition)
9th Edition
ISBN:9780134746241
Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Chapter1: The Study Of Minerals
Section: Chapter Questions
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A. A solidified lava flow containing zircon mineral crystals is present in a sequence of rock layers that are exposed in a hillside. A mass spectrometer analysis was used to count the atoms of uranium-235 and lead-207 isotopes in zircon samples from the lava flow. The analysis revealed that 71% of the atoms were uranium-235, and 29% of the atoms were lead-207. Refer to Figure 8.10 to help you answer the following questions. 1. About how many half-lives of the uranium-235 to lead-207 decay pair have elapsed in the zircon crystals? 2. What is the absolute age of the lava flow based on its zircon crystals? Show your calculations. 3. What is the age of the rock layers beneath the lava flow? 4. What is the age of the rock layers above the lava flow? B. Astronomers think that Earth probably formed at the same time as all of the other rocky materials in our solar system, including the oldest meteorites. The oldest meteorites ever found on Earth contain nearly equal amounts of both uranium- 238 and lead-206. Based on Figure 8.10, what is Earth's age? Explain your reasoning. C. If you assume that the global amount of radiocarbon (formed by cosmic-ray bombardment of atoms in the upper atmosphere and then dissolved in rain and seawater) is constant, then decaying carbon-14 is continuously replaced in organisms while they are alive. However, when an organism dies, the amount of its carbon-14 decreases as it decays to nitrogen-14. 1. The carbon in a buried peat bed has about 6% of the carbon-14 of modern shells. What is the age of the peat bed? Explain. 2. In sampling the peat bed, you must be careful to avoid any young plant roots or old limestone. Why? D. Zircon (ZrSiO,) forms in magma and lava as it cools into igneous rock. It is also useful for absolute age dating (Figure 8.10). 1. If you walk on a modern New Jersey beach, then you will walk on some zircon sand grains. Yet if you determine the absolute age of the zircons, it does not indicate a modern age (zero years) for the beach. Why? 2. Suggest a rule that geologists should follow when they date rocks according to radiometric ages of crystals inside the rocks. E. An "authentic dinosaur bone" is being offered for sale on the Internet. The seller claims that he had it analyzed by scientists who confirmed that it is a dinosaur bone and used carbon dating to determine that it is 400 million years old. Give two reasons why you should be suspicious of this bone's authenticity. (See Figures 8.9, 8.10). 1. 2.
Transcribed Image Text:A. A solidified lava flow containing zircon mineral crystals is present in a sequence of rock layers that are exposed in a hillside. A mass spectrometer analysis was used to count the atoms of uranium-235 and lead-207 isotopes in zircon samples from the lava flow. The analysis revealed that 71% of the atoms were uranium-235, and 29% of the atoms were lead-207. Refer to Figure 8.10 to help you answer the following questions. 1. About how many half-lives of the uranium-235 to lead-207 decay pair have elapsed in the zircon crystals? 2. What is the absolute age of the lava flow based on its zircon crystals? Show your calculations. 3. What is the age of the rock layers beneath the lava flow? 4. What is the age of the rock layers above the lava flow? B. Astronomers think that Earth probably formed at the same time as all of the other rocky materials in our solar system, including the oldest meteorites. The oldest meteorites ever found on Earth contain nearly equal amounts of both uranium- 238 and lead-206. Based on Figure 8.10, what is Earth's age? Explain your reasoning. C. If you assume that the global amount of radiocarbon (formed by cosmic-ray bombardment of atoms in the upper atmosphere and then dissolved in rain and seawater) is constant, then decaying carbon-14 is continuously replaced in organisms while they are alive. However, when an organism dies, the amount of its carbon-14 decreases as it decays to nitrogen-14. 1. The carbon in a buried peat bed has about 6% of the carbon-14 of modern shells. What is the age of the peat bed? Explain. 2. In sampling the peat bed, you must be careful to avoid any young plant roots or old limestone. Why? D. Zircon (ZrSiO,) forms in magma and lava as it cools into igneous rock. It is also useful for absolute age dating (Figure 8.10). 1. If you walk on a modern New Jersey beach, then you will walk on some zircon sand grains. Yet if you determine the absolute age of the zircons, it does not indicate a modern age (zero years) for the beach. Why? 2. Suggest a rule that geologists should follow when they date rocks according to radiometric ages of crystals inside the rocks. E. An "authentic dinosaur bone" is being offered for sale on the Internet. The seller claims that he had it analyzed by scientists who confirmed that it is a dinosaur bone and used carbon dating to determine that it is 400 million years old. Give two reasons why you should be suspicious of this bone's authenticity. (See Figures 8.9, 8.10). 1. 2.
A. Analyze this fossiliferous rock from New York. 1. What index fossils from Figure 8.9 are present? 2. Based on the overlap of range zones for these index fossils what is the relative age of the rock (expressed as the early, middle, or late part of one or more periods of time)? 3. Using Figure 8.9, what is the absolute age of the rock in Ma (millions of years old/ago), as a range from oldest to youngest? A X1 B. Analyze this fossiliferous rock from Ohio. 1. What index fossils from Figure 8.9 are present? 2. Based on the overlap of range zones for these index fossils, what is the relative age of the rock (expressed as the early, middle, or late part of one or more periods of time)? 3. Using Figure 8.9, what is the absolute age of the rock in Ma (millions of years old/ago), as a range from oldest to youngest? B C. Analyze this fossiliferous sand from Delaware. 1. What index fossils from Figure 8.9 are present? 2. Based on the overlap of range zones for these index fossils what is the relative age of the rock (expressed as the early, middle, or late part of one or more periods of time)? 3. Using Figure 8.9, what is the absolute age of the rock in Ma (millions of years old/ago), as a range from oldest to youngest? c X1 D. Using Figure 8.9, re-evaluate the geologic cross section in Figure 8.2 based on its fossils. 1. Which one of the contacts (surfaces) between lettered layers is a disconformity? 2. A system is the rock/sediment deposited during a period of time. What system(s) of rock is/are completely missing at the disconformity? 3. What amount of absolute time in m.y. (millions of years) is missing at the disconformity? m.y. E. What geologic event occurred during the Mesozoic Era in the region where Figure 8.3 is located? Explain.
Transcribed Image Text:A. Analyze this fossiliferous rock from New York. 1. What index fossils from Figure 8.9 are present? 2. Based on the overlap of range zones for these index fossils what is the relative age of the rock (expressed as the early, middle, or late part of one or more periods of time)? 3. Using Figure 8.9, what is the absolute age of the rock in Ma (millions of years old/ago), as a range from oldest to youngest? A X1 B. Analyze this fossiliferous rock from Ohio. 1. What index fossils from Figure 8.9 are present? 2. Based on the overlap of range zones for these index fossils, what is the relative age of the rock (expressed as the early, middle, or late part of one or more periods of time)? 3. Using Figure 8.9, what is the absolute age of the rock in Ma (millions of years old/ago), as a range from oldest to youngest? B C. Analyze this fossiliferous sand from Delaware. 1. What index fossils from Figure 8.9 are present? 2. Based on the overlap of range zones for these index fossils what is the relative age of the rock (expressed as the early, middle, or late part of one or more periods of time)? 3. Using Figure 8.9, what is the absolute age of the rock in Ma (millions of years old/ago), as a range from oldest to youngest? c X1 D. Using Figure 8.9, re-evaluate the geologic cross section in Figure 8.2 based on its fossils. 1. Which one of the contacts (surfaces) between lettered layers is a disconformity? 2. A system is the rock/sediment deposited during a period of time. What system(s) of rock is/are completely missing at the disconformity? 3. What amount of absolute time in m.y. (millions of years) is missing at the disconformity? m.y. E. What geologic event occurred during the Mesozoic Era in the region where Figure 8.3 is located? Explain.
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