Name: _______________________
Unit 7: Evolution
“Life changes over time”
Date: _________________
Period: __________
m&ms Half-Life Activity
Introduction: Recall that half-life is the amount of time it takes for one half of a
sample of radioactive material to decay. From this, we can determine how old
rocks (and the fossils within them) are, which in turn provides clues to how life on
Earth has changed since it began about 3.5 billion years ago. Now, we all know
that m&ms are not elements, nor are they radioactive, but they do provide a
good model for how radioactive decay works (not to mention, they’re yummy!)
Purpose: The goal of this activity is to simulate the process of radiometric dating
to better understand how half-lives can be used to calculate the ages of rocks
and fossils.
Materials: m&ms, paper cup, paper towel
Procedure:
1. Wash your hands!
2. Double check the number of
m&ms in your cup.
3. Shake the cup a couple of
times, then empty the m&ms
onto the paper towel.
4. Count the # of original m&ms
(the m is facing up). Record
this # in the data table and
put them back in the cup.
5. Count the # of decayed
m&ms (the m is facing down).
Record this # in the data table
(decayed m&ms are edible).
6. Repeat steps 3-5 until one or
no m&ms remain.
7. Make a graph showing how
the # of original m&ms
changes over time (based on
the # of tosses) and answer
the analysis questions on the
back of this page.
# of
tosses
(half-life)
# of original
m&ms with m
facing up
# of decayed
m&ms with m
facing down
0
60
0
1
2
3
4
5
6
7
8
9
10
Analysis Questions:
1. What is radioactive decay? Why is it useful?
2. Approximately what percentage of the m&ms decayed after each toss?
How does this demonstrate half-life?
3. When will the radioactive decay of an element stop? Explain.
4. There is a radioactive version of potassium that has a half-life of 1.3 billion
years. Predict how long it will take for 100% of the potassium to decay.