Building the Critical Zone

Lily Eligator, Virginia Polytechnic Institute and State University

Initial Publication Date: May 13, 2025

Summary

Students construct their own model Critical Zones using mason jars and layered materials representing bedrock, saprolite, soil, and vegetation. As each layer is added, facilitators explain its function and significance. The completed jar models, including a seedling, are taken home with care instructions.

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Context

Audience

Elementary/middle school science

Skills and concepts that students must have mastered

This is an introduction activity, so no concepts are required, but students should be able to follow instructions clearly and patiently work one step at a time with the whole class.

How the activity is situated in the course

This is a very easy introduction activity so students can understand what the critical zone is actually made up of.

Goals

Content/concepts goals for this activity

This activity covers the layers of the critical zone, and (if scaled) can cover weathering, nutrient cycling, water cycle, and erosion.

Higher order thinking skills goals for this activity

Students should be able formulate hypotheses and draw conclusions based on prior information given.

Skills goals for this activity

For younger students, fine motor skills will be used.

Description and Teaching Materials

Materials:
1 mason jar per student
1-2 bedrock rocks (rocks that can fill the bottom of the mason jar)
Approx. 20 pebbles per student to fill the bottom of the jar
Sand
Potting soil
1 seedling per student

Activity:

Main Activity:
Introduce the critical zone briefly and explain that we're going to build our own version of the critical zone that will support life.
Make sure to break down the words CRITICAL and ZONE - to help students build up the definition.
Explain each part of the critical zone, getting as in depth as you want. Examples:
Bedrock - what can bedrock be made of? How deep is bedrock? Does everywhere on the planet have bedrock?
Saprolite - how quickly does bedrock weather into saprolite? Is saprolite always made out of the same thing as the bedrock? Where does the word saprolite come from?
Soil - what types of soil are there? How do you know what soil type is which? Is sand soil?
Once you've explained that part of the critical zone, add it to the container and "build" the CZ step by step. Explain to students that they can take care of their critical zone after this.

Finish by explaining why weathering is important to you (if time!)
Full Lesson Plan (Acrobat (PDF) 3.2MB May13 25)

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