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South Carolina ETV
1101 George Rogers Boulevard
Columbia, SC 29201-4761
Phone: 803-737-3545

Rock of Ages (Grades 6-8)

Master Teacher

Ida Wideman

Time Allotment

Two 45-minute class periods

Overview

Geologists cannot look at a rock structure or outcrop and determine their ages. More formal techniques are involved in the determination of the age of these natural structures.

Geologists use the process of radioactive decay of certain elements that are found in some rocks to help with their geologic age. Radioactive decay occurs in the nucleus of the atom. During this process, energy is released, and a new element, called a daughter element, is formed. Each radioactive element has its own half-life. Half-life is the time it takes for half of the atoms in the element to change into the decay product, the stable element. For example, uranium 238 decays through a series of 14 steps; the end product is lead 206.

Using video, the Internet and hands-on activities in this lesson, students will learn how to determine the age of rocks and fossils based on radioactive decay data.

Subject Matter

Science

Learning Objectives

Students will be able to:

• Determine the age of a rock based on radioactive decay data.
• Observe (through simulation) the radioactive decay of a fictitious element.

South Carolina Standards

(These Standards are available online at http://www.myscschools.com/offices/cso)

Fossils provide important evidence of how life and environmental conditions have changed. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common. Most of the species that have lived on the Earth no longer exist.

e. Explain how scientists use technology to date rocks and fossils (e.g., radioactive dating).

Media Components

Video

Historical Geology: A Glimpse of the Earth’s Past , “How Do Scientists Discover Information about Earth’s Past.” This video provides information on different methods of dating rocks.

To access the video segment, log on to your account at ETV’s StreamlineSC Web page (http://etv.streamlinesc.org). In the search by keyword box, type Historical Geology: A Glimpse of the Earth’s Past and hit go.

Click the series title and then download the following video segment to your computer desktop and preview it. “How Do Scientists Discover Information about the Earth’s Past” runs for two minutes.

Natural Phenomena: Rocks, Fossils and Earth History , “Rocks and History.”

This video provides information on a technique that geologists use to date rocks and fossils.

Like you did above, in the search by keyword box, type Natural Phenomena: Rocks, Fossils and Earth History and hit go. Click the series title and then download the following video segment to your computer desktop and preview it. “Rocks and History” runs for three minutes and 40 seconds.

(Note to Teacher: If you don’t have an account with ETV’s StreamlineSC, check with your media specialist or Instructional Technologist about signing up for your own account).

Web Sites

Radioactive Decay

http://www.mines.utah.edu/~ggapps/radiation/radiation.html

This is an interactive Web site in which the decay process for four different radioactive decay series can be observed.

Half-Life—A Useful Concept

http://vcourseware.calstatela.edu/VirtualDating/files/2.0_HalfLife.html

This is an interactive graph that simulates the passage of time in a mineral.

Materials

Per group: Learning Activity

• Shoe box with lid
• 100 cubes
• Felt tip pen
• Activity Sheet 1 (one sheet per group)

Per class: Culminating Activity

• 600 Styrofoam cups (8 oz. suggested. Students should contribute.)
• 12 feet of dark yarn
• 4 ' x 6 ' sheet of white bulletin-board paper
• Hand-held calculator
• Cup diagram

Equipment

• Computer

Prep for Teachers

• Prior to this lesson, bookmark all of the Web sites used in the lesson on each computer in the classroom. In addition, load the Shockwave plug-in, available at http://www.macromedia.com, and Windows Media Player, available at the Microsoft.com Web site (http://www.microsoft.com/downloads/details.aspx?FamilyID=e0175119-9a5b-44c3blde-9b2a9aa6cff6&DisplayLang=en)

Introductory Activity Preparation

Prepare and copy the children’s stories to be used in this activity. Each group gets a different story. Use familiar stories such as The Three Bears, Little Red Riding Hood, The Three Little Pigs, Snow White and the Seven Dwarfs, Sleeping Beauty, or any other stories of your choice.

After you’ve selected a story, cut the entire story into large strips. Remove two or three main points (strips) from the story. Shuffle the remaining strips and place them in an envelope or bag.

Have students to work in groups of four for this activity.

Learning Activity Preparation

Have students work in pairs, or in groups of three.

You will need 100 cubes per group. Any small cube-shaped objects will suffice; however, cubes made of some materials will last longer, while others might cost less. Some suggestions include sugar cubes, math cubes, dice or home-made cubes constructed of wood or Styrofoam. Gather the rest of the items listed under Materials for this activity.

When using media, provide students with a Focus for Media Interaction, a specific responsibility to complete during or after viewing of video, Web sites, or other multimedia elements.

Introductory Activity

Step 1: Distribute a children’s story to each group. Tell the students that they are to distribute pieces of the story to each group member. Tell them that they will find a familiar children’s story in each envelope. Tell them that they are to use the strips to put the story together again. Let the students determine how they are going to put the story in order. Do not tell the students that some pieces will be missing from their stories. Let the students “discover” that a piece or two is missing.

Step 2: Ask the students what they discovered about the stories. (They should say, “We could not find all of the pieces for the story.”) Then tell them that the strips represent rock structures. This is exactly what happens when geologists are working with rock structures and fossils. Many important pieces will be missing and this makes it very difficult to date rocks and fossils.Geologists call this absolute age or time.

Step 3: Thiswill be a goodtime to introduce techniques that geologists use to date rocks and fossils. Tell the students that they will study absolute age and radiometric dating. Explain to students that absolute age is the actual age of an object. When students insert the missing pieces from the story, they have determined the absolute age of the story. Radiometric dating is a technique (process) that geologists use for calculating the absolute age of rocks and minerals that contain radioactive isotopes.

Step 4: Tell students that they are going to learn more about dating. Provide them with a Focus for Media Interaction, asking them to answer the questions that pertain to the graph on the screen. Warn them to raise their hands and wait for you to call on them.

Step 5: Pull up the bookmark for Half-Life Web site at http://vcourseware.calstatela.edu/VirtualDating/files/2.0_HalfLife.html.

When you see the animated graph, click and move the slider to the right to simulate the passage of time. Explain to students what is involved in this process and tell them that they will use the information on the graph to answer the questions that follow on the page.

Learning Activities

Step 1: Provide students with a Focus for Media Interaction, by asking them to observe the technique that geologists use to date rocks and fossils. PLAY the video clip “Rocks and History” from the series Natural Phenomena: Rocks, Fossils and Earth History that you downloaded to your computer desktop. When you see the photograph of fossils and the narrator says, “Fossils form . . .” tell the students to observe and listen as the narrator gives an explanation for half-life. Also, tell students to listen for information that is being given on the technique that geologists use to date rocks and fossils. Tell the students that they will watch the entire video. It lasts three minutes and 40 seconds. At the end, you will see a scientist holding a fossil.

Step 2: Break your students into pairs or groups and distribute the materials for the activity, along with a copy of Activity Sheet 1 for each group or pair.

Step 3: Tell students to mark only one side of each cube with a felt-tip pen. (Note toTeacher: If you are using dice cubes, choose a number with which to work.)

Step 4: Tell the students to place 100 cubes in the box.

Step 5: Tell the students to hold the lid tightly and turn the box over twice and then remove the lid.

Step 6: Tell the students to take out all cubes that have their marked-side turned up. These cubes represent atoms that have decayed into daughter elements. In the data table beside Trial 1, record the number of cubes removed. Subtract this from the number of cubes remaining. Record the second number in the other block of Trial 1.

Step 7: Tell the students to repeat Steps 5 and 6 until 12 trials have been completed or until all the cubes have been removed.

Step 8: Tell the students that they are going to observe as they manipulate a radioactive series decay in action. Provide your students with a Focus for Media Interaction, asking them to raise their hands and select a decay series to click on. (Note to Teacher: The simulation can be run in the Animate mode which will automatically choose the time step for the process.)

Step 9: Pull up the bookmarked Radioactive Decay Web site http://www.mines.utah.edu/~ggapps/radiation/radiation.html

(Note to Teacher: Be sure to bookmark this before class because it takes a few minutes to load. When the very first screen changes to a screen with a gray background, you will see a graph on the left of the screen and an activity log on the right side of the screen. Become familiar with the on-screen instructions before using the program.)

Step 10: Tell the students to use the data in the chart on page one of Activity Sheet 1 to make a graph on page 2 of the sheet. On the vertical axis, plot the number of cubes remaining each time. On the horizontal axis, plot the trial numbers.

Step 11: Tell the students to connect the points they have plotted.

Culminating Activity

Step 1: (Note to Teacher: The data that was collected in the Learning Activity will be used for this activity. Tell the students to keep their activity sheets.) Distribute the items under Materials. Tell the students to stack a number of cups equal to the class average of parent atoms for each trial.

Step 2: Tell the students to connect the stacks by placing the yarn on each top cup of the stack with either tape or a small weight. Now you have constructed a bar-graph using the data from the entire class.

Step 3: Tell the students to construct a large graph on a 4 ' x 6 ' sheet of white bulletin-board paper. Tell the students to make horizontal increments (x-axis) the width of a Styrofoam cup.

Step 4: Tell the students to make vertical increments (y-axis) the height of the lip of the cup. See the cup diagram.

Step 5: Tell the class that many trials of an experiment will give a more accurate representation of the results than one or two trials.

Step 6: Tell the students thatthey will construct a bar graph using the same kind of data, to compare with the line graph they plotted in the Learning Activity.

Step 7: Tell the students that the bar graph will be based on data collected from the entire class.

Step 8: Have students to return to their desks. Provide them with a Focus for Media Interaction, asking them to observe the geologists on-screen and be able to tell you the techniques they are using to date rocks. They should also be able to discuss the process.

Step 9: PLAY the video clip “How Do Scientists Discover Information about Earth’s Past” from the series Historical Geology: A Glimpse of the Earth’s Past. Tell students to LISTEN and to observe and to silently read all captions on the screen. You will see a black screen at the end. Tell the students to write the name of the technique that geologists use to date rocks and to explain the process in their notebooks.

Cross-Curricular Extensions

Language Arts: Have students research information on some of the early scientists that worked in the field of radioactivity.

Math: Have students find examples of charts that contain information on radioactive isotopes and decay products with about 3 half-lives. Have the students calculate and extend the charts to several additional half-lives.

Social Studies: Have students to research the social and economic impact of radioactivity on the economy.

Health: Research the use of Magnetic Resonance Imaging and CAT scans and how they are beneficial to humans. Discuss how radioactivity is involved in these.

Community Connections

• Invite representatives to visit the classroom from places such as the Savannah River Site, Westinghouse or nuclear power stations. Ask them to discuss with students how they are able to use radioactive materials and how they keep themselves safe at work.

Student Materials

Per group:

• Shoe box with lid
• 100 cubes
• Felt tip marker
• Activity Sheet 1 with chart, graph and questions
• Cup Diagram

Per Class:

• 8 oz. Styrofoam cups
• 12 feet of dark yarn
• Bulletin-board paper (4 ' x 6 ')