8., You start with 800 parent atoms of a particular radioactive type, which decays to give stable offspring. You wait just long enough for two half lives to pass. You should expect to have how many parent atoms remaining (on average):, A., 400.
B., 200.C., 100.D., 50.E., 25.
After one half-life, you’ve gone from 800 parents to 400 parents; after a second half-life you go from 400 parents to 200. . (Typical studies of radioactive decay use many more atoms, to avoid statistical fluctuations, but the question says “on average”, so we asked you about 800 rather than 800,000,000,000,000 to make the math easier.), Points Earned:, 1/1
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:, A., Uniformitarian techniques if the deposit is old, and counting of annual layers if the deposit is young.B., Uniformitarian techniques.C., Either counting of annual layers or radiometric techniques if the deposit is old (more than about 100,000 years), and radiometric techniques if the deposit is young (less than about 100,000 years).D., Either counting of annual layers or radiometric techniques if the deposit is young (less than about 100,000 years), and radiometric techniques if the deposit is old (more than about 100,000 years).E., Counting of annual layers if the deposit is old (more than about 100,000 years), and radiometric techniques if the deposit is young (less than about 100,000 years).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