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Grades: 9-12
Author: Vicki Peplin
Source: Ideas gathered from: Radiometric Dating Activity and Determining the Age of Fossils
This lesson is designed to help students understand the concepts of radioactive dating to help determine the approximate age of fossils and rocks. After this lesson students will have an understanding of how materials undergo radioactive decay and that the rate of decay allows scientists to predict the approximate age of the specimen. This lesson is geared to help take the "mystery" out of scientific dating of rocks and fossils.
What should students know as a result of this lesson?
What should the students be able to do as a result of this lesson?
Each student group will need the following:
Engagement
Have students work in groups of 2-3 per group. The teacher may assign groups or allow students to pick with whom they would like to work. These groups will be used throughout the remainder of the lesson. Go over the "proper use of materials for their intended purpose" policy to remind students of the difference between acceptable and unacceptable behaviours in class. Follow the directions from the Determining the Age of Fossils website for activity 2a. Before the lesson, the teacher should copy the data tables found in Figures 2 and 3 (on the website) and paste the tables to a student worksheet so that the students have a place to record their data. On the back of the worksheet the teacher should copy and paste the three after-activity questions found next to Figure 3 on the website. Once all individual data are recorded have participants share their data in a way that all participants can observe (on a large white board) so that a class average can be calculated. At the end of the activity the groups may eat their M&Ms.
Assessment: Monitor students' work to check that they are carrying out procedures carefully, making observations, and recording data accurately. Redirect their attention to the task, as needed.
Exploration
Follow the directions on the Radiometric Dating website. Before the lesson the teacher will need to make a student activity worksheet with the data table, graph, and follow-up questions found on the website. Also, the teacher will need to assemble the five different bead bags and place them in various locations around the classroom. The amount of each type of bead for each bag is found in the directions on the website.
Assessment: Monitor students' work to check that they are carrying out procedures carefully, making observations, and recording data accurately. Redirect their attention to the task, as needed.
Explanation
Students report their findings. Each team shares their data from the activity worksheets. Discuss with the class as a whole the student responses to the end of the activity questions from the "Engagement" and "Exploration" sections of the learning cycle. During the discussion explain to students how this decay is at a set rate for a given element and that by measuring the percent rate of decay scientists can accurately predict the approximate age of a fossil or rock. This is not to be confused with the statistical probability of the change in the population over time as demonstrated with an individual group's data during the M&Ms activity. Note that the average of all of the groups' data more closely resembles the statistical probability of the change over time not the individual group's data.
Assessment: Have students explain in their own words the concept of half-life in radioactive decay, demonstrate how the rate of radioactive decay and the buildup of the resulting decay product are used in radiometric dating of rocks, and compare and contrast individual statistical data results to the class average of various statistical data results to determine reliability and predictability of the two groups.
Elaboration
Have students research a radioactive isotope of their choice and find the following information:
Types of radioactive isotopes:
Assessment: Teacher should develop a rubric to assess students' research papers.
Students should have a basic knowledge of the parts of an atom especially concerning protons and neutrons.
NGSS Standards:
Common Core Standards:
National Standards:
Ohio Standards:
Vocabulary:
Math Connections:
During the engagement activity students observe what occurs in a population of M&Ms over time due to random chance. The statistical probability of the M&M "decay" is 50% per each half-life but the actual data may not reflect the theoretical probability. Students may confuse this random change of events with the non-random decay of radioactive isotopes. Stress the fact radioactive decay is not random and is highly predictable based upon past empirical data.
The small beads and M&Ms could be choking hazards or a projectile hazard. Therefore, the teacher should state and enforce a no throwing rule of materials. The M&Ms can be eaten by the students at the end of the activity. Make sure to know any food related allergies of the students before handing them the candy. If such allergies occur, use a substitute material such as pennies.
This content is applicable to the real world due to the fact that it deals with the scientific dating of rocks and fossils found on the planet.
At the end of the lesson each student will be presented with his/her own fossil. This fossil will have information containing how much of the parent and daughter isotopes were found as well as the accepted half-life of the radioactive isotope. Using a graph that relates percentages of parent isotope levels to number of half-lives students will determine the approximate age of the fossil.
Example data set:
Potassium-40 = 12 isotopes
Argon-40 = 88 isotopes
Half-life = 1.25 billion years
Answer: Using the graph from the Exploration activity, this radioactive isotope has undergone three half-lives thus making the fossil (1.25 * 3 =) 5.25 billion years old.
Grouping Suggestions: The teacher should assign small groups (2-3 students) to ensure diversity within the groups. Teacher discretion is advised especially in the areas of mathematical abilities.
Pacing/Suggested Time: Three class periods (approximately 45-50 minutes for each period).
Radioactive Dating Assessment Worksheet
The activity worksheets need to be created by the teacher with information based off of the websites.
Worksheet #1: This worksheet will correlate with the "engage" portion of the module and will need to include Figure 1 from the Determining the Age of Fossils website. The back of the worksheet will correlate with the "explore" portion of the module and will need to include Figure 2 and Figure 3 from the Determining the Age of Fossils website.
Worksheet #2: This worksheet will correlate with the "elaborate" portion of the module and will need to include the data table, graph, and follow-up questions found on the Radiometric Dating website.