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d. What is the half-life for carbon-14? How many half-lives occur in 50,000 years, the limit of age dating by this method? What fraction of the origi- nal C14 remains after 50,000 years? (Calculate as accurately as possible.) 10.

d. What is the half-life for carbon-14? How many half-lives occur in 50,000 years, the limit of age dating by this method? What fraction of the origi- nal C14 remains after 50,000 years? (Calculate as accurately as possible.) 10.

Chemistry by OpenStax (2015-05-04)
Chemistry by OpenStax (2015-05-04)
1st Edition
ISBN:9781938168390
Author:Klaus Theopold, Richard H Langley, Paul Flowers, William R. Robinson, Mark Blaser
Publisher:Klaus Theopold, Richard H Langley, Paul Flowers, William R. Robinson, Mark Blaser
Chapter21: Nuclear Chemistry
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Problem 44E: Isotopes such as 26Al (half-life: 7.2105 years) are believed to have been present in our solar...
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sented by Precambrian time? By the Cenozoic era d. Humans first appeared on Earth about 2 million years ago and recorded history consists of the last 10,000 years. What percentage of the age of the Earth do each of these represent? 8. Radiometric Age Dating. a. What are the three different particles given off by radioactive decay of isotopes? What happens to the isotopes in the process? Explain. b. Thorium-232 decays to form lead-208 by a 10-step reaction in this order a, ß, ß, a, a, a, a, ß, ß, a. In the same form as shown for the 92U238 to 82Pb206 reaction (see Figure 10.5), show this for the 90Th232 to 82Pb208 reaction. c. Calculate the value of A, the decay constant, for U238/Pb206, U235/Pb207, and Th232/Pb208. Include the correct units for A. d. What is the half-life for carbon-14? How many half-lives occur in 50,000 years, the limit of age dating by this method? What fraction of the origi- nal C¹4 remains after 50,000 years? (Calculate as accurately as possible.) e. Why is Rb-Sr dating more accurate in dating some metamorphic rocks if muscovite is used rather than biotite? Explain. What is meant by "resetting the clock" in this respect? If a muscovite sample indicated an age of 138 million years and a biotite sample from the same rock indicated 122 million years, what does this indicate relative to the previ- ous question? Explain. f. Why is the K-Ar dating method particularly sub- ject to errors if considerable metamorphism of the rock has occurred? In a sample metamorphic rock the U238/Pb206 date made on a zircon crystal was 275 million years, whereas the K-Ar date on it V i 9. Gre Ge a. b. 10. G Fi ar Ja a. b C
Transcribed Image Text:sented by Precambrian time? By the Cenozoic era d. Humans first appeared on Earth about 2 million years ago and recorded history consists of the last 10,000 years. What percentage of the age of the Earth do each of these represent? 8. Radiometric Age Dating. a. What are the three different particles given off by radioactive decay of isotopes? What happens to the isotopes in the process? Explain. b. Thorium-232 decays to form lead-208 by a 10-step reaction in this order a, ß, ß, a, a, a, a, ß, ß, a. In the same form as shown for the 92U238 to 82Pb206 reaction (see Figure 10.5), show this for the 90Th232 to 82Pb208 reaction. c. Calculate the value of A, the decay constant, for U238/Pb206, U235/Pb207, and Th232/Pb208. Include the correct units for A. d. What is the half-life for carbon-14? How many half-lives occur in 50,000 years, the limit of age dating by this method? What fraction of the origi- nal C¹4 remains after 50,000 years? (Calculate as accurately as possible.) e. Why is Rb-Sr dating more accurate in dating some metamorphic rocks if muscovite is used rather than biotite? Explain. What is meant by "resetting the clock" in this respect? If a muscovite sample indicated an age of 138 million years and a biotite sample from the same rock indicated 122 million years, what does this indicate relative to the previ- ous question? Explain. f. Why is the K-Ar dating method particularly sub- ject to errors if considerable metamorphism of the rock has occurred? In a sample metamorphic rock the U238/Pb206 date made on a zircon crystal was 275 million years, whereas the K-Ar date on it V i 9. Gre Ge a. b. 10. G Fi ar Ja a. b C
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