RADIOMETRIC DATING WORKSHEET Show work for all problems NAME ____________ DATE _____ HOUR __ Use the general decay curve to answer the following: 1. A fossil log sample was sent to the lab for a radioactive determination. The was used. Of the original 240 grams of 14C only 15 grams of 14C remain. 14 C → 14N radioactive decay How many half lives has this sample been through? _______________ How many grams of 14N must be in the log? What is the age of the log? _____________________ 2. Gneiss was submitted for radioactive analysis. Certain minerals in the gneiss were found to contain 40 K. The 40 K → 40Ar method was used. The results of the analysis found 40K= 20g and 40Ar = 300 g. What is the D/P ratio? ______________ How many half lives has this sample been through? _________ What is the age of the gneiss? ______________ Is there a problem with this answer? Explain _____________________________________________ 3. A sample of granite was analyzed using the 3H →3He method (half life= 12.3 years). Results of the granite are 3H = 2g and 3He = 100g. What is the D/P ratio? _____ What is the age of the granite? _______________________ 4. A sample of gneiss was analyzed using the 235U → 207 Pb method. 235 U = 2g and 207Pb= 12g What is the D/P ratio? _________ What is the age of the gneiss? _____________ 5. A rock sample is analyzed using the 14C → 14N method. If the D/P ratio is 100, how old is the sample? _______________ 6. A sample of granite is analyzed using the 40K → 40 Ar method. Of the original 300 of potassium only 75 grams remain. How many half lives has this granite been through? _______________ How many grams of argon are in this granite? _____________________ How old is this sample? _____________ What geologic era did this granite form in?