Difficulty:

Grade Level:

**Using M&Ms candies, this exercise will demonstrate the process of radioactive decay and its uses for determining the age of a substance. **Submitted by James Rathjen.

Procedure:

- Collect at least 100 M&M’s. Assume that each of the M&M’s starts out as heads up and that coins that are heads up are radioactive parent atoms.
- We are assuming that initially there are 100 parent atoms and 0 daughter atoms. If you begin with a different number of coins than 100, enter the number of parent atoms (M’s) with which you start. Trial 0 represents the number of parent and daughter atoms in a substance when it first forms.
- Put the M&M’s in a cup and dump them out of onto a table. Count the number of parent atoms (M’s) and record the number under No. of Parent Atoms under trial 1. Count the number of daughter atoms (blank) record that number under No. of Daughter atoms.
- Put the remaining parent atoms (M&M up) into the cup. The daughter atoms (no M&M’s) should not be included since they are no longer radioactive. Dump the M&M’s in the cup into the table. Record the number of remaining parent atoms. Add the daughter atoms to the pile of daughter atoms from the previous trial(s). Record the total number of daughter atoms.
- Repeat the previous step until there are no remaining parent atoms. Fill in chart.

- Using your data and what you have read about the assumptions of radiometric dating answer the following questions.
- Graph your data. On the horizontal axis, plot the trial number (half life). On the left vertical axis, plot the percentage of parent atoms remaining. On the right vertical axis, plot the percentage of daughters atoms present. Use two different colors or line schemes. Label the curves C14 and N14.
- Assuming that the time span between each trial is 5730 years, what happens to the abundance of parent atoms over time?
- What happens to the abundance of daughter atoms over time?
- Does the percentage by which the abundance of parent atoms changes during each trial approximately correspond as predicted by theory? Explain your answer.
- If you found a substance in which 87.5% of the parent/daughter total consisted of daughter atoms, what percentage would you predict would be parent atoms? How many half-lives have passed?
- Knowing the number of half-lives that have passed from question 5 and the half-life (H) of your hypothetical substance (which is 5,730 years), calculate its age.
- You encounter an archeological site in which you find timbers which contain 75% nitrogen 14 and 25% carbon 14. Carbon 14 is the parent atom. How much nitrogen 14 do we assume was originally present?
- You encounter a site that has 3% Carbon 14 (_______________ % Nitrogen 14). What is the age?
- How many half-lives have passed if a sample has 95% Nitrogen 14 in it? How old is it?
- Very briefly summarize how radiometric dating works.