Radiometric Dating Worksheet When radioactive isotopes (parent - P) decay, they produce daughter products (D) at a constant rate, called the half-life (T). Example: if we start with 100 atoms of the parent, after one half-life, there will be 50 parent atoms remaining and 50 daughter atoms newly made. After another half-life (two half-lives), there will be 25 parent atoms remaining and now 75 daughter atoms. Each parent-daughter isotope pair has its own half-life. To achleve the above example with U-238 takes 9 billion years (two half-lives). To achieve the above example with C-14 takes 11,400 years (two half-lives). The daughter atom of C14 is N14,K40 is Ca40, and U-238 is Pb206. In the geologic environment, we use a mass spectrometer to count the number of Parent and Daughter atoms in a closed-system (ike minerals crystallizing from magmas), and use the relative proportions to find out how old the closed-system is. Answer the foliowing questions 1. To date the age of a shell found in an old Native American fishing village, which isotope pair would you measure, C-14 or U-238? Why? (14. bccause 2. If you want to date a meteorite, which isotope pair would you measure? Why? U238,because 3. If you want to date lava flows on an old lava flow on Kauai (probably about 8m.y.), which isotope pair would you measure? Why? 4. If you want to date zircon crystals in ancient sandstones in Australia, which isotope pair would you measure? Why? 5. If the C-14:N-14 ratio in a shell in a sandstone was found to be 1:3, how old is the shell? 6. If the U-235:Pb-207 ratio in a zircon in a sandstone was found to be 1:3, how old is the zircon? 7 If the K-40:Ca-40 ratio in a zircon in a granite was found to be 1:1, how old is the sample? K40 half-life =1.3 billion yrs. 8. If the U-238:Pb-206 ratio in a zircon in a lava flow was found to be 3:1, how old is the flow