Absolute Dating
Table 1
Table 2
Table 3 and Graph 10, 8, 4, 0
Lab Question Answers Questions: 1, 2 (on table 5: a, b, c, d), 3, 4, 5, 6, 7, 8 8, 6.4, 3.2, 0
Conclusions 4, 3, 2, 0
Sources / Citations 2, 1.6, 1.2, 0
Activities for Lab 2: Absolute Dating
Activity 1: Isotope Pairs and Half Lives
NOTE: No additional materials are needed for this activity.
Instructions
Geologists use a variety of isotope pairs to date rocks and other materials using radioactive decay. In this activity, you will use the half-life values of the main isotope pairs to calculate the length of time represented by each half-life.
Table 1: Radioactive Isotope Pairs and Half-lives lists the various isotope pairs used on the left, and the length of one half-life for each pair. You are to determine the amount of time represented half-life values of 2, 3, 4, and 5. To do this, multiply the length of time for one half-life by the number of half-lives represented in each column. You will use this information to answer questions in other parts of this lab.
Table : Radioactive Isotope Pairs and Half-lives
Parent > Daughter Isotope Time needed for 1 half-life (years) Time needed for 2 half-life (years) Time needed for 3 half-life (years) Time needed for 4 half-life (years) Time needed for 5 half-life (years)
40K >40A 1.25 billion
238U > 206Pb 4.468 billion
235U > 207Pb 703.8 million
87Rb > 87Sr 48.8 million
14C > 14N 5,730
Activity 2: Using Probability to Predict Decay Rate
NOTE: No additional materials are needed for this activity.
Instructions
Scientists use mathematical concepts such as probability, to help them determine the theoretical outcomes for their models. In this activity, you are going to use the probability of the results of a coin toss to make predictions for the decay rate of a substance.
You will not actually be tossing a coin until Activity 3; in this activity you will use the probability of getting a heads to complete the data table. Since there are only two sides to a coin, the probability of getting a heads is one out of two – or one half. This means that if you flip a coin 10 times, the probability of getting a heads is 5 out of 10. The probability of the total number of heads varies with the amount of times you flip a coin, the probability of heads will be one half of the total flips. In the first row we will start at 100 because the “sample” is brand new. In the second row, we divide the value of Parent Material in the row above by 2 in order to get the half-life; this will also be the value for the Daughter Products; and for the final column you will simply sum the Daughter Products that have occurred.
You will be recording your probability predictions on Table 2: Predicting Decay Rates. The first part of the table has been completed for you; use these values to fill in the remaining cells.
On this table:
Time represents the number of half-lives that have passed since the beginning
Parent Material is the number of coins/flips you start with for each Half-life Time interval
Daughter Products is the number of Tails you flipped for each Half-life Time Interval
Cumulative Daughter Products column is a running total of how many daughter flips you have had (the values in this column should increase from 0 to 100).
Table : Predicting Decay Rates
Time
Representing Number of Half-lives Parent Material:
Predicted Number of Parents remaining for each time interval Daughter Products:
Predicted number of Daughters produced for each time interval Cumulative Total of Daughter
Products
0 100 0 0
1 50 50 50
2 25 25 75
3
4
5
6
7
Activity 3: Collecting Probability Data
Materials needed: Coin
Instructions
In activity 2, you predicted the probability of material remaining for seven half-lives. In this activity, you will be actually flipping the coin to collect real data that more closely reflects natural processes – nature rarely follows the rules exactly, usually because there are more variables involved than we humans are aware of. You will Record your results on Table 3: Decay Rates Based on Flipping a Coin. Notice that results obtained from two other fictional students who did this activity are included. You will be graphing all three sets of data.
Remember, for each flip: Heads = Parent Material, Tails = Daughter Products
For each Half-life Time Interval, start with the number of Parents left from the previous time interval. Repeat this procedure until there is no Parent Material Remaining, recording your results on Table 3: Decay Rates Based on Flipping a Coin.
Table : Decay Rates Based on Flipping a Coin
Your Data “Jason’s” Data “Brisell’s” Data
Time Parent Material Daughter Products
Cumulative Daughter
Products Time Parent Material Daughter Products
Cumulative Daughter
Products Time Parent Material Daughter Products
Cumulative Daughter
Products
0 100 0 0 0 100 0 0 0 100 0 0
1 1 48 52 52 1 49 51 51
2 2 28 20 72 2 26 23 74
3 3 5 23 95 3 15 11 85
4 4 4 1 96 4 6 9 94
5 5 2 2 98 5 5 1 95
6 6 1 1 99 6 2 3 98
7 7 0 1 100 7 1 1 99
Now that you have your data and the data of two additional students (Jason and Brisell), you are to graph your results.
Set up your graph in the following manner:
X-axis is the Manipulated/Independent Variable: Time values from 0 to 7, label your axis
Y-axis is the Responding/Dependent Variable: 0 to 100% of Parent Material, label your axis
Graph your results, using different colors or line types for the four sets of data. Include a key with your graph that indicates the symbol/color for each set of data:
Your Predictions from Activity 2
Your Data from Activity 3
“Jason’s” Data
“Brisell’s” Data
GRAPH:
Lab Questions for Lab 2: Absolute Dating
Activity 1: Isotope Pairs and Half Lives
1. Examine Table 4: Useful Geologic Material for Determining Age below. Using what you learned in Activity 1, explain how the Useful Dating Range was determined.
Table : Useful Geologic Materials for Determining Age
Parent > Daughter
Isotope
Applicable Geologic Materials Useful Dating range
40K >40A Potassium bearing minerals in igneous or
metamorphic rocks, e.g., Potassium-feldspar, Muscovite, Hornblende 100,000 to 4.5 billion years
238U > 206Pb &
235U > 207Pb Zircon bearing igneous or metamorphic rocks 10 million to 4.6 billion years
87Rb > 87Sr Potassium bearing minerals commonly felsic igneous rocks 10 million to 4.5 billion years
14C > 14N
aka radiocarbon dating Organic, carbon bearing materials, such as wood or charcoal. Mostly for archeological applications. 100 to 30,000 years
2. Table 5: List of Geologic Materials is a list of geologic material and their approximate age. For each material, indicate which pair or pairs of Isotopes would be best used to determine the actual age. You don’t need to include the subscriipts – use: K-Ar; U-Pb, Rb-Sr and/or C-N
Table : List of Geologic Materials
Material Information / Observations Best isotope pair(s) to use
a. Gneiss Probably Precambrian, contains K-feldspar, muscovite and hornblende
b. Granite Probably from the Paleozoic, contains K-feldspar, muscovite and hornblende
c. Zircon Grain Found in Paleozoic sediment – grain is older than the sediment
d. Cotton cloth Found at an ancient human burial site in Europe
NOTE on Geologic Time: Precambrian (4.5 billion to 541 million years ago), Paleozoic (541 to 64 million years ago)
3. Explain why all methods cannot be used to date all of the materials listed in Table 5.
Activity 2: Using Probability to Predict Decay Rate
4. Describe the process or reasoning you used to make your predictions.
Activity 3: Collecting Probability Data
5. Examine your Prediction Data in Part 2 and the data from the three (3) Trials in this section. Are the results exactly the same? Describe why this is so.
6. Describe the general shape of the lines you plotted on your graph.
7. How do the shapes of the four lines compare? If they are very different, give an explanation of why they are different. If they are similar in shape, explain why this is so.
8. This lab was designed to help you understand “radioactive half-life”. In your own words, define the principle of “radioactive half-life”.
Conclusion for Lab 2: Absolute Dating
Give a short summary of what you did in each section, include science concepts addressed, any challenges you faced, and conclusions you can make based on the data you collected.
Overall, what did you learn from doing this lab in regards to using Absolute Dating to determine the age of rocks? What questions do you now have?
Your response:
Your citation(s):
PROVIDED QUESTION TEMPLATE
Name:
Date
Lab title
Lab Partner (state “N/A” when no partner is used)
Table 1: Radioactive Isotope Pairs and Half-lives
Parent > Daughter Isotope Time needed for 1 half-life (years) Time needed for 2 half-life (years) Time needed for 3 half-life (years) Time needed for 4 half-life (years) Time needed for 5 half-life (years)
40K >40A 1.25 billion
238U > 206Pb 4.468 billion
235U > 207Pb 703.8 million
87Rb > 87Sr 48.8 million
14C > 14N 5,730
Table 2: Predicting Decay Rates
Time
Representing Number of Half-lives Parent Material:
Predicted Number of Parents remaining for each time interval Daughter Products:
Predicted number of Daughters produced for each time interval Cumulative Total of Daughter
Products
0 100 0 0
1 50 50 50
2 25 25 75
3
4
5
6
7
Table 3: Decay Rates Based on Flipping a Coin
Your Data “Jason’s” Data “Brisell’s” Data
Time Parent Material Daughter Products
Cumulative Daughter
Products Time Parent Material Daughter Products
Cumulative Daughter
Products Time Parent Material Daughter Products
Cumulative Daughter
Products
0 100 0 0 0 100 0 0 0 100 0 0
1 1 48 52 52 1 49 51 51
2 2 28 20 72 2 26 23 74
3 3 5 10 95 3 15 11 85
4 4 4 1 96 4 6 9 94
5 5 2 2 98 5 5 1 95
6 6 1 1 99 6 2 3 98
7 7 0 1 100 7 1 1 99
GRAPH:
Activity 1: Isotope Pairs and Half Lives
1. Examine Table 4: Useful Geologic Material for Determining Age below. Using what you learned in Activity 1, explain how the Useful Dating Range was determined.
Table 5: List of Geologic Materials
Material Information / Observations Best isotope pair(s) to use
a. Gneiss Probably Precambrian, contains K-feldspar, muscovite and hornblende
b. Granite Probably from the Paleozoic, contains K-feldspar, muscovite and hornblende
c. Zircon Grain Found in Paleozoic sediment – grain is older than the sediment
d. Cotton cloth Found at an ancient human burial site in Europe
3. Explain why all methods cannot be used to date all of the materials listed in Table 5.
Activity 2: Using Probability to Predict Decay Rate
4. Describe the process or reasoning you used to make your predictions.
Activity 3: Collecting Probability Data
5. Examine your Prediction Data in Part 2 and the data from the three (3) Trials in this section. Are the results exactly the same? Describe why this is so.
6. Describe the general shape of the lines you plotted on your graph.
7. How do the shapes of the four lines compare? If they are very different, give an explanation of why they are different. If they are similar in shape, explain why this is so.
8. This lab was designed to help you understand “radioactive half-life”. In your own words, define the principle of “radioactive half-life”.
Conclusion for Lab 2: Absolute Dating
Citation(s) of Sources Used:
