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Determining the Age of Fossils

Grades: 5-8
Author: Vicki Peplin
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Abstract

Module Description

How do scientists really know how old a fossil or a rock is? This is a question that many students and teachers have and this module is designed to answer this mystery. Participants will follow the learning cycle with hands-on/minds-on activities to investigate the phenomena of radioactive decay while enjoying the "sweet taste" of their success.


Objectives

  • Participants will use half-life properties of isotopes to infer the age of different rocks and fossils.
  • Participants will 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.
  • Participants will explain the concept of half-life in radioactive decay, and demonstrate how the rate of radioactive decay and the buildup of the resulting decay product are used in radiometric dating of rocks.
  • Participants will be experience the hands-on/minds-on and learning cycle teaching techniques throughout the module with the expectation that these processes will then be translated into the participants' classrooms via an implementation lesson plan.

Materials

Each participant group will need the following:

  • 5 small plastic bags (to be filled by teacher with beads according to the procedure)
  • Approximately 500 plastic beads of different colors
  • A calculator
  • 100 M&Ms
  • Activity worksheets (presenter created from websites, see preparation)

Procedures

Engagement

Have participants work in groups of 2-3 people per group. The presenter may assign groups or allow participants 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 model for participants of how to address the difference between acceptable and unacceptable behaviors in the classroom. Follow the directions from the Determining the Age of Fossils website for activity 2a. Before the lesson, the presenter should copy the data tables found in Figure 2 and 3 (on the website) and paste the tables to a participant worksheet so that the participants have a place to record their data. On the back of the worksheet the presenter 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 participants' 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 presenter will need to make a student activity worksheet with the data table, graph, and follow-up questions found on the website. Also, the presenter 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 participants' 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

Participants report their findings. Each team shares their data from the activity worksheets. Discuss with the group as a whole the participant responses to the end of the activity questions from the "engagement" and "exploration" sections of the learning cycle. During the discussion, explain to participants 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.

Also discuss with the participants the two major teaching techniques highlighted in this module: the learning cycle and hands-on/minds-on learning. Information about the learning cycle and hand-on/minds-on learning can be found on the AGPA's best practices website http://uakron.edu/cpspe/agpa-k12outreach/best-teaching-practices/learning-cycle.

Assessment: Have participants 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

Part I (optional, if time allows):

Have participants research a radioactive isotope of their choice and find the following information:

  • Parent isotope
  • Daughter isotope
  • Half-life
  • Fossils and/or rocks dated with this isotope
  • Where in the world the fossils and/or rocks were located
  • How old the fossils and/or rocks are according to the isotope

Types of radioactive isotopes:

  • Uranium-238
  • Uranium-235
  • Thorium-232
  • Rubidium-87
  • Potassium-40
  • Samarium-147
  • Carbon-14

Assessment: Presenter should develop a rubric to assess participants' research papers.

Part II

At the end of the module have participants complete the Lesson implementation template individually and then discuss with a peer or with the group as a whole what they plan on taking back to their classrooms. Plans should focus on a topic related to the content of this experience with an emphasis on using the best practice teaching strategies of hands-on/minds-on learning and the learning cycle.

Assessment: The presenter will conduct an informal assessment of participants' learning during the discussion(s). If possible, the presenter could visit the participants' classes while they are using their implementation lesson developed during the module.


Rationale

This module is designed to model two of AGPA's best practices: hands-on/minds-on learning and the learning cycle through the teaching of the concepts of radioactive decay. Once participants feel comfortable with these teaching techniques they can then lead their own students through the same processes to further the students' understanding of the concepts.


Science Standards

NSES Content Standard A: Science as Inquiry

  • Mathematics is essential in scientific inquiry. Mathematical tools and models guide and improve the posing of questions, gathering data, constructing explanations and communicating results.

NSES Content Standard D: Earth Science

  • Geologic time can be estimated by observing rock sequences and using fossils to correlate the sequences at various locations. Current methods include using the known decay rates of radioactive isotopes present in rocks to measure the time since the rock was formed.

NSES PROFESSIONAL DEVELOPMENT STANDARD A: Professional development for teachers of science requires learning essential science content through the perspectives and methods of inquiry.


Best Teaching Practices

  • Learning Cycle
  • Hands-on/Minds-on Learning

Time Frame

Preparation Time: 30 minutes

Module Time: 2-3 hours


Preparation

Before teaching this module the presenter must construct two worksheets (by downloading information from the listed websites) for the participants to use during the activities as well as assemble the beads into bags and place in different locations around the room. Notify participants in advance, to bring their curriculum guides and or textbooks to facilitate their development of an implementation plan.

Worksheet # 1: This worksheet will correlate with the "engage" 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 "explore" portion of the module and will need to include the data table, graph, and follow-up questions found on the Radiometric Dating website.

Bag directions: The five different bags of beads will correlate with the "explore" portion of the module and the directions of how many beads should be placed in each bag are found on the Radiometric Dating website.


Safety

The M&Ms can be eaten by the participants at the end of the activity. The beads and bags can be reused from class to class.


Assessment

Assessments are given after each part of the learning cycle in the procedures. If possible, the presenter could visit the participants' classes while they are using their implementation lesson developed during the module.


Explanation of Science

Vocabulary:

  • Isotope: An alternate form of an element due to a change in the number of neutrons. Examples include C-12 and C-14.
  • Parent Isotope: The unstable radioactive isotope that will decay over time.
  • Daughter Isotope: The stable un-radioactive isotope that the parent isotope decayed into.
  • Radioactive decay: Radioactive isotopes that are unstable and change over time to become more stable.
  • Half-life: The probable rate of nuclear decay of a radioactive isotope.
  • Probability: the statistical chance than an event will occur.

Math Connections:

  • During the engagement activity participants 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 that actual data may not reflect the theoretical probability. Participants may confuse this random change of events with the nonrandom decay of radioactive isotopes. Stress the fact radioactive decay is not random and is highly predictable based upon past empirical data.

Handouts

None Available for this Module


Extensions

USGS Radiometric Time Scale at http://pubs.usgs.gov/gip/geotime/radiometric.html

Uranium information at http://education.jlab.org/itselemental/ele092.html

Thorium information at http://education.jlab.org/itselemental/ele090.html

Rubidium information at http://education.jlab.org/itselemental/ele037.html

Potassium information at http://education.jlab.org/itselemental/ele019.html

Carbon information at http://education.jlab.org/itselemental/ele006.html


Lesson Implementation Template

Download Lesson Implementation Template: Word Document or PDF File


Equity

Throughout this module the presenter should be aware that there are a variety of learning styles and needs from the participants. Any and all accommodations should be made by the presenter as needed. Also, some participants may be allergic to the M&Ms. Therefore, alternative materials may be used such as pennies, two-sided tokens, etc.


Resources

None available for this module


References

Radiometric Dating Activity

Determining the Age of Fossils