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?