Absolute Dating - String
Student Worksheets (Science)
Basic facts:
 The string represents radioactive atoms.
 Cutting the string represents radioactive decay occurring.
 When radioactive decay occurs, energy is released during this process.
 If an element is radioactive it is also referred to as unstable.
 Only half of the total elements will become daughters every ½ life.
 Absolute dating can only be used on igneous, metamorphic rock and once living
things.
 The initial radioactive/unstable element is called the PARENT, while decay
products are referred to as DAUGHTERS.
Assumptions we are going to make:
 Both parents and daughters are atoms
 String’s half-life equals 200 years
 Cut string represents DAUGHTER ATOMS (stable)
 Uncut string represent PARENT ATOMS (radioactive/unstable)
Questions:
Pre-Experiment Questions:
If a 50 cm string represents a 100% of radioactive parent atoms:
1. Predict how many cuts (Half-lives) you will be able to make on the string. Justify
your reasoning.
2. What are the factors that will keep you from reaching 0% parent and/or 100%
daughter?
3. Based on your answers from questions 1 and 2 create a hypothesis using the “if,
then, because” format. (Will you be able to reach 0% parent?)
Procedure:
1. Cut a piece of string that is 50 cm. One 50 cm string represents 100%
unstable parent atoms.
2. Place the string in your hand and count for 5 seconds, to represent the
string’s half-life of 200 years.
3. Then fold the string in half and cut at the fold. (Taking away half of the
string). One part of the cut string represents material that has become
stable (Daughters).
4. Measure the remaining (left side) string (Parents) and record this in the
Chart.
5. Continue to cut the string until you can no longer accurately cut the string
in half with the equipment given.
6. Repeat sets 3-5 until you have completed your chart or you cannot cut
again.
7. Record results in chart (These results should mimic radioactive half-life
theory).
String Chart (Science)
Number of half
life’s
Years
Length of Left side of
string in Cm
(Parents)
%
Parents
Total Length of Cut
String in Cm
(Daughters)
% Daughters
0
1
2
3
4
5
6
7
8
Post-Experiment Questions:
1. Was there any parent string left? If so, why didn’t you continue to cut it?
2. How accurate was your prediction from pre-experiment question#1?
3. Theoretically will you ever get to zero Parents? Justify.
4. How does this mimic a scientist measuring stable and unstable atoms?
5. Create a thesis statement using your hypothesis. Remember to include data to
support your claim.
Extension Question: Why can’t absolute dating be used to age sedimentary rock?
Student Worksheets (Math)
Basic facts:
 The Skittles represents radioactive atoms.
 When radioactive decay occurs, energy is released during this process.
 If an element is radioactive it is also referred to as unstable.
 Theoretically only half of the remaining Parent elements can become daughters every ½
life but results will vary experimentally because the process occurs randomly.
 Absolute dating can only be used on igneous, metamorphic rock and once living things.
 The initial radioactive/unstable element is called the PARENT, while decay products are
referred to as DAUGHTERS.
Assumptions we are going to make:
 Skittle’s half-life equals 200 years
 Label side of skittles will represents DAUGHTERS (stable)
 No label side of skittles will represent PARENTS (radioactive/unstable)
Questions:
Pre-Experiment Questions:
1. If you created a Parent vs Time graph for this scenario, would the graph be linear or
non-linear? Justify your reasoning.
2. Make a prediction, using a graph, of what the half-life would theoretically look
like, if you start with 50 parents at time zero. If only half of the total can become
stable every half-life.
Procedure: (I would recommend using hand sanitizer on your hands and getting
out a sheet of paper to pour the skittles on)
1. Count out a total of 50 skittles for your group. Make sure each skittle has a
label.
2. Place them in your cup. This represents the number of atoms of radioactive
elements at formation, or in the case of C-14.
3. On your chart put 50 parents down for time 0.
4. Gently shake the cup for 5 seconds, to represent the skittles half-life of 200
years.
5. Then, pour the contents on your sheet of paper.
6. Remove skittles that have a label showing. These are atoms that have become
stable (Daughters).
7. Record results in chart.
8. Repeat until all skittles have become stable but 1. Each pour counts as one
half-life (200 years).
9. When all the parents have decayed but 1, put all the skittles back in cup and
repeat steps 4 to 8 for a total of three times.
10. In Chart 4, calculate the averages for the number of parents for each half-life.
11. Graph results of Chart 4 (Graph provided).
Chart 1
Number of
half life’s
0
1
2
3
4
5
6
7
8
9
10
11
Years
Number of
Radioactive
Skittles
(Parents)
%
Parents
Number of
Stable
Skittles
(Daughters)
%
Daughters
Chart 2
Number of
half life’s
0
1
2
3
4
5
6
7
8
9
10
11
Years
Number of
Radioactive
Skittles
(Parents)
%
Parents
Number of
Stable
Skittles
(Daughters)
%
Daughters
Chart 3
Number of
half life’s
0
1
2
3
4
5
6
7
8
9
10
11
Years
Number of
Radioactive
Skittles
(Parents)
%
Parents
Number of
Stable
Skittles
(Daughters)
%
Daughters
Chart 4: Averages
Number Years
of half
life’s
0
1
2
3
4
5
6
7
8
9
10
11
Number of
Radioactive
Skittles
(Parents)
Graph Number of Parents vs. Time
Post-Experiment Questions:
1. Was the graph linear? If not what type of graph is it?
2. Is it proportional? Justify.
3. In actuality, will all the radioactive material ever become stable? Does your
skittles graph agree? Why or why not?
4. Using the data from your science class, graph on the above graph.
Remember to make a key to the graph. Compare the “string” data with the
“skittle” data and describe the similarities and differences that you found.
Give at least 2 examples.
5. Which experiment best represents theoretical radioactive decay?
6. Which experiment best represents experimental radioactive decay?
7. What would need to happen to get your experimental results closer to the
theoretical results? (For example, how could you alter the experiment?)
Extension Questions:
Complete the chart below for three different elements. Show all work on your
own paper.
Parent Left
Half-life in years
1/8
30,000
1.3 billion
1/4
Age in years
10,000
3.9 billon