Relative dating activity: read clay rock layers like a geologist, 6–8
What it is: a middle school activity where students build four flat layers of colored modeling clay with paper fossils between them, add a fault cut and a vertical intrusion, then swap models and work out the order of events. Students apply superposition (older layers lie below younger ones) and cross-cutting relationships, as geologists do with real rock walls.
Time: about 40 minutes. Grade: 6–8.
Materials: four colors of modeling clay per group, a rolling pin or round bottle, small paper fossil shapes, a plastic knife, a strip of a fifth clay color for the intrusion, index cards, and a recording sheet.
- Review the idea: in undisturbed rock, the bottom layer formed first. Anything that cuts through layers is younger than the layers it cuts.
- Groups flatten four clay layers and stack them, placing one paper fossil between two of the layers.
- With the plastic knife, cut a slanted line through all layers and slide one side down a little: a fault.
- Press a strip of the fifth color straight up through the layers on one side: an intrusion of melted rock.
- Groups write their secret order of events on an index card, turned face down.
- Groups swap models and list the order they think happened, from oldest to youngest.
- Check against the card and discuss any disagreements.
Safety: plastic knives only, cut on a board, and wash hands after handling clay.
Differentiation: students who need support build only the layers and the fault. Students who are ready add an erosion surface (a wavy cut across the top) and a new layer on top of it. English learners can use "___ is older than ___ because ___."
Quick check: ask: "A fault cuts through layers A, B and C. Is the fault older or younger than layer B?" (Younger.)
For more ideas at this grade, browse the other free activities on the Hub.
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About this resource
- Shared by
- @UpOnlyLearning · Curriculum team
- Posted
- Oct 31, 2026
- Type
- Lesson plan
- Grade
- Grades 6–8
- Subject
- Science
- Language
- English
- License
- Free for classroom, co-op and tutoring use. Please don't resell.