7.You are dating a lava flow by the potassium-argon system. However, the offspring in this system are leaking out of the minerals. Which is accurate?A.You will think that the lava flow is younger than it really is, but you will be able to detect the error by comparing concentrations of offspring from the edges and centers of grains.B.You will think that the lava flow is younger than it really is, and you will have no way to detect your error.C.You will think that the lava flow is older than it really is, and you will have no way to detect your error.D.You will think that the lava flow is older than it really is, but you will be able to detect the error by comparing concentrations of offspring from the edges and centers of grains.E.You will get the age exactly right without worrying about any complications.Argon-40 leakage will make the lava flow appear young even if the flow is old; however, the edges of grains will lose more argon-40 than will the centers, pointing to the source ofthe error.Points Earned:1/1Correct Answer:AYour Response:A8.You start with 200 parent atoms of a particular radioactive type, which decays in a single step 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):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:1/1Correct Answer:EYour Response:E9.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:
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- Spring '12
- Geology, Quiz, rocks