Introduce this lesson by showing the model of the cranberry bog. Ask students to compare the model to what they would see if they visited a bog. Then raise these questions:
“What do you think we might we see below the surface of the bog?”
“How might we find out for sure what is under the bog’s surface?”
Students are likely to suggest digging into the soil.
- Acknowledging that digging into the soil to see it is a reasonable idea, hold up a core sample (X or Z). Explain that one way scientists probe what is underneath the surface of the ground is to dig a core out of the soil. Point out that the model core sample has different layers. Each different soil is formed in a different way, so core samples are like secret geological codes that can help us understand what was going on in a given place when the soil was made and put down in that spot. (Different locations reveal unique patterns.)
Let students know that in this lesson, they will learn what’s beneath the bog—and how it got there. Introduce the challenge of this lesson: To examine three different model core samples and decide which one represents a cranberry bog core sample. Explain that to solve this challenge, students will need some information about what happens to create the layers underneath the bog. Tell students that you will show them a presentation of the bog’s history to help them gather this information. (Also, if they have participated in the Exploring Cranberries lesson, Cranberry Connections, review what they recall about the bog history. Some information will be repeated in this presentation, but there will also be new information that students should listen and watch for.)
- Explain to the students that following the slide show, the class will have enough information to create a bog history timeline. Randomly distribute the timeline index cards among the groups. Explain that each card captures a moment in the past of a cranberry bog, and that this past stretches back at least 10,000 years.
- While introducing the Beneath the Bog movie presentation, instruct students to pay special attention to the part of the program that relates to the card(s) they have just received. Encourage students to notice what came before and after the moment in time that is summarized on their own timeline card. (To notice what comes before their assigned timeline moments, they’ll have to pay attention carefully.) Let them know that after the presentation, each group will be responsible for suggesting where on a blank timeline the class should place the cards they have been given.
- Have students watch the Beneath the Bog Movie Presentation show in small groups at stations or as a whole class.
- Conduct a class discussion to complete a timeline. As each group presents its card(s) to the whole class, let them suggest where they think the card should go—at the beginning of the 10,000 year timeline, at the end (present day), or somewhere in the middle? Attach the cards to the timeline. Give other groups opportunities to suggest changes or ask questions.
- As different groups contribute their cards, rearrange the cards as necessary, referring back to the Beneath the Bog Movie Presentation resource as needed to clarify points of confusion.
- Once you have the timeline in place, play the slide show again to check the timeline for accuracy. Make corrections to the timeline as necessary.
- Re-introduce the cores sample, pointing out that it is “a geologist’s sort of timeline”. You may find the following talking points helpful:
- A core sample helps us “see” into the past: It is a collection of soil and other material set down over a long period of time. The different materials and layers give clues to what was going on at different times.
- A helpful analogy might be the case of someone going on vacation for a whole summer. If the mail carrier makes a stack of the mail, adding to it with every delivery, eventually there would be a tower of catalogues, newspapers, and other material. Help students reason out that if the pile were kept in order, the mail that arrived first would be at the bottom of the pile. The closer to the top of the pile, the closer we get to today’s mail. Similarly, the closer we are to the surface of the bog, the closer we are to the present.
- Review the timeline cards for clues about what the different soil types indicate about what was happening at a given time. Which types of soils are mentioned in the timeline? (clay, gravel, sand, peat) Conduct a class discussion around the following questions:
- Which of these would be deep at the bottom of the bog core? Why do you think so?
- Which would be in the middle? Why do you think so?
- Which would be near to the surface? Why do you think so?
- Again refer to the model core sample and collect students’ observations of the core. At this time, hand out small samples of the actual soil materials (if available) so students can better understand the models.
- Distribute the model core samples so that each group has one sample. On the board, provide a key to the different materials and the soil types they represent. Distribute one Decoding the Core Student Worksheet per student. Although each small group should work together to examine their core’s layers, each student should individually record and label the layers in the core. Students can use the key on the sheet to determine what type of soil is in each layer.
- After several minutes, have groups exchange their samples, so that each group can repeat the observation with a different core sample. Repeat again for the third sample.
- Have small groups “decode” the information in the samples to determine which one--X, Y, or Z—they think most closely corresponds to the timeline of the bog’s past. Discuss as a whole group, encouraging students to state the reasons for their conclusions.
- Show students your model bog. Reinforce the idea that we can only see what’s at the surface; no core is immediately available to us when we walk a bog. However, we can take a core sample. Demonstrate with your own fourth, empty plastic tube. You will need to twist the tube back and forth slightly to help ease its way through the layers. Be sure to go all the way through the clay at the bottom to ensure that the clay in the core sample can act as a plug to keep the gravel in.
- Note: If you were unable to acquire plastic tubes and are using the alternative set-up, settle for slicing the bog model like a piece of cake, trying to lift out the multi-layered piece intact. Even if this fails, you will have made a cut into the model and revealed the layers.
- Pull out the core/expose the layers. Discuss student observations and establish which mystery sample matches the bog layers. Invite discussion and requests for clarification.
- Wrap up with the following discussion points:
- How does the core sample show the bog’s past?
- How has the past made the present cranberry bogs possible?
- What questions from the Cranberry Questions Wall sheet have they addressed in this lesson?
- What new questions would they like to add?