8. You start with 200 parent atoms of a particular radioactive type, which decays in a singlestep to give a stable offspring, and you start with none of those stable offspring. You wait just long enough for two half lives to pass. You should expect to have how many offspring atoms (on average): A. 200. B. 150. C. 100.
D. 50. E. 25. After one half-life, you’ve gone from 200 parents to 100, and 100 offspring have been made. In the second half-life, you go from 100 to 50 parents, and that makes another 50 offspring. Adding the additional 50 to the 100 from the previous half-life gives 150 offspring. (Typical studies of radioactive decay use many more atoms, to avoid statistical fluctuations, but the question says “on average”, so we asked you about 200 rather than 200,000,000,000,000 to make the math easier.) Points Earned: 0/1 Correct Answer: B Your Response: D 9. You are asked to assign as accurate a numerical age as possible (how many years old) to a sedimentary deposit. You would be wise to use: If you want an absolute date (number of years) rather than older/younger, you can count layers for young things, or use radiometric techniques for young things or for old ones. Uniformitarian calculations aren’t very accurate. Points Earned: 1/1
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