1. Introduce this lesson by showing a model cranberry marsh. Ask students to compare the model to what they would see if they had visited a marsh.
Have students consider the following questions:
- “What do you think we might we see below the surface of the marsh?”
- “How might we find out for sure what is under the marsh surface?” Students are likely to suggest digging into the soil.
Acknowledge that digging into the soil is a reasonable idea; explain that scientists probe underneath the surface of the ground to reveal soil horizons. Core samples have different layers depending on how the soil formed. The strata or layers reveal secret geological codes that help us understand the environmental history of a given place. Different locations may reveal unique patterns.
2. Randomly distribute the timeline index cards among the groups. Explain that each card captures a moment in the past of a cranberry marsh, and that this past stretches back at least 13,000 years.
3. 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 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.
4. 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 soil profile 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.
5. 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? (gravel, sand, peat and muck) Conduct a class discussion around the following questions:
- Which of these would be deep at the bottom of the marsh? 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?
6. Hand out small samples of the actual soil materials (if available) so students can better understand the models. Explain to students that they will make their own model of a soil profile in a plastic container. To create the profile, add materials in the following order:
- ¾-inch layer of small landscape gravel to represent bedrock
- ½-inch sand deposit from glacier
- ½-inch mix of sphagnum and kitty litter, peat/muck layer
- 1/2-3/4 inch of sand representing the layer
- Scatter pieces of cranberry vine and push into topmost sand layer
7. Wrap up with the following discussion points:
- How does the soil sample show the marsh’s past?
- How has the past made the present cranberry marshes possible?