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Lesson Plans
I'm Late, I'm Late, for a Radioactive Date!
Student Sheet #3

Name: ______________________________________

Amount of Pu
in grams
# of half-lives
(time periods)
Time in Years Fraction of Pu left Percent of Pu left
100 g 0 0 (start) 1 100%
  1 5 years 1/2 50%
  2 10 years 1/4  
  3 15 years    

What is the general formula for determining half-life? _________________

Interactive Site:

Answer the following:

1. Generated in the upper atmosphere, C-14 makes up only ____% of all carbon atoms.

2. Because of interaction and exchange with atmosphere and oceans, all living tissue maintains a _______ proportion of C-14. After death, the amount of C-14 begins to ______________.

3. A C-14 date estimates the time since the death of once-living things, up to about _________years.

4. What percent of original C-14 can be found in a sample after 10 HL? ____

5. Why is the daughter product, N-14, not retained by a specimen?  _______


6. Use the decay calculator to determine the age of a rock that has 87% of its mass. __________BP.

7. Use the calculations for the above in BP, substitute it into the calculator,
and determine the date in A.D. _________A.D.

8. Explain why the amount of C-14 produced in the Earth's upper atmosphere from cosmic rays striking N-14 is or is not constant over time.





9. What would be the age if you used the calibration or correction curves for the time in question 6?