Hands-on Activity Exploring the Earth’s Critical Zone with Edible Model Cross Sections

Learning Objectives

After this activity, students should be able to:

• Explain what the critical zone is.
• Describe the layers within the critical zone.
• Explain why the critical zone is critical to the health of the environment.
• Understand that all life exists within the critical zone.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Materials List

Each student needs:

• clear 3 oz plastic cup (for example)
• unbroken Nilla Wafer
• tablespoon of butterscotch chips
• 3-4 tablespoons of chocolate pudding (pudding cups work well)
• plastic spoon
• 2 gummy worms
• 3-5 Oreo cookies (preferred), or chocolate Teddy Grams
• tablespoon of shredded coconut
• 1-2 gummy bears
• small lollipop, like Dum Dum (optional)

For the entire class to share:

• laptop/computer with projector to present the Exploring Earth’s Critical Zone Presentation
• The Living Landscape by Eric Parrish and Suzanne Anderson: https://www.amazon.com/Living-Landscape-Discovering-Critical-Zone/dp/1630763969
• Sandwich or quart size plastic bags with zip closure (to smash Oreo cookies or Teddy Grahams)
• 2-3 drops of green food coloring (to color shredded coconut)
• freezer gallon bag (to mix coconut and green food coloring)
• plastic or metal spoons for measuring and spooning out ingredients (that can be shared amongst the students)
• plastic gloves for teacher to hand out food materials
• (optional) rolling pin or rubber mallet (to smash Oreo cookies)

Worksheets and Attachments

Pre-Req Knowledge

Students should have a basic understanding of elementary Earth Science education.

Introduction/Motivation

[Optional: Read The Living Landscape by Eric Parrish and Suzanne Anderson to the class.]

[Display the Exploring Earth’s Critical Zone Presentation to the class.]

(Show slide 2) What is the critical zone? The Critical Zone is like the Earth’s living skin. It’s a “living” skin because it is within this thin layer that all life occurs. We live in the critical zone and so do all the trees, plants, animals, birds, flowers, and all other life on land. This special layer is called the “critical zone” because it is critical for life on Earth.

(Display slide 3) If we could slice into the Earth and see inside, we would see all the layers that form our planet. At the very center is the inner core which is surrounded by the outer core and then the mantle. The top layer of rock (above the mantle) is called the crust. How deep the crust goes into the Earth varies by continent, but the crust is ONLY 12 to 40 miles thick throughout the world. Remember, the diameter of the Earth is about 7,900 miles!

Think of it this way: if the Earth were reduced to the size of a peach, then the skin of the peach would be about the thickness of the crust of the Earth. Now that is very thin compared to the size of the Earth!

If we zoom in closer to the top of the crust, the area we are talking about today a thin layer that sits on top of the crust.  The critical zone extends from the tops of the trees down through the soil through the ground water to the bedrock.

(Display slide 4) Why do you think the critical zone is critical for life? (Let students offer answers.) We depend on the critical zone for our air, water, food, and shelter. By studying the critical zone, scientists and engineers can help ensure that life on Earth continues to survive, grow, and thrive.

(Show slide 5) Let’s take a closer look at the critical zone!

Procedure

Background

The Earth's critical zone is the “heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air, and living organisms regulate the natural habitat and determine the availability of life-sustaining resources” The Critical Zone, surface and near-surface environment, sustains nearly all terrestrial life.

Critical zone science is an interdisciplinary field of research exploring the interactions among the land surface, vegetation, and water bodies, and extends through the soil, the subsurface, and saturated groundwater zone. Critical Zone science is the integration of Earth surface processes such as landscape evolution, weathering, hydrology, geochemistry, and ecology. These processes impact mass and energy exchange necessary for biomass productivity, chemical cycling, and water storage.

The critical zone is studied by multiple scientific and academic communities who examine various aspects zone that can lead to a better understanding of these complex systems. In addition, studying and understanding the critical zone is imperative to many different engineering fields including environmental engineering, agricultural engineering, and civil engineering.

Before the Activity

• Read and review the material in book The Living Landscape.
• Collect all materials for the activity.
• Ensure students are not allergic to any of the activity materials.
• Mix a small amount of green dye with the shredded coconut in a gallon size freezer bag.

With the Students

1. Read through the Introduction/Motivation section.
2. Have students answer the following questions in small groups:

1. What is rock?
2. What is bedrock?
3. How is soil created?
4. Why do you think soil is important?

3. As a group, discuss the above questions. Lead students to the following answers:

1. What is rock? (Answer: Rock is a natural, solid material made up of one or more minerals. The Earth is made up of rock.)
2. What is bedrock? (Answer: Bedrock is hard, solid rock underneath soil, sand, and gravel.)
3. What is soil? (Answer: Soil is a mixture of rock pieces, water, air, living and dead things. Soil supports plant life that is necessary for life on Earth.)
4. How is soil created? (Answer: Soil is formed over long periods of time. It forms from bigger rocks that have been weathered, or worn down, by wind, rain, sun, snow, and chemical reactions.)
5. Why do you think soil is important? (Answer: plants and animals live and grow in soil.)

4. Have students wash their hands thoroughly.
5. Have students gather their materials and place them on their working surface. 

   

6. Show Slide 6 of the Exploring Earth’s Critical Zone Presentation. Explain: The critical zone is the layer where rock, soil, water, air, and living organisms meet and interact to make life possible! The critical zone is made up of different layers. To see these layers we need to look at a cross section of the critical zone. Who knows what a cross section is? (Let students offer answers.) A cross section is the shape we get if we were to cut a straight line into the Earth (running from the surface all the way down to the bedrock) and then move away all the material in front of it. This is a cross section of the critical zone. Starting from the bottom of the critical zone the first layer (or the lowest layer) we have is bedrock. Bedrock is hard, solid rock that has been created through plate tectonics. It lies beneath all of the other layers in the critical zone. Here are some examples of bedrock that have come to the very surface of the earth.
7. Direct students to place 1 Nilla wafer at the bottom of their clear 3 oz. cup.

   

   This will be their bedrock layer.
8. Explain: Starting at the bottom of our cross section we have bedrock. Bedrock is hard, solid rock. It lies beneath all the other layers. We are going to use the Nilla wafer to represent the bedrock because it is solid, not in pieces.
9. Show Slide 7 of the Exploring Earth’s Critical Zone Presentation. Say: The layer above the bedrock layer is called saprolite or weathered rock. This layer is made up of bigger rock chunks. This layer forms over thousands of years as the top of the bedrock breaks down into smaller and smaller pieces by a process called weathering. Weathering is wearing down and breaking apart the rocks. In this case, the rock is broken down by chemical weathering. This means that the bedrock is broken down by chemical alterations or changes to the rock. This can be from water or other minerals seeping down to the top of the bedrock and then reacting with the rock. These changes make the bedrock break apart.  This weathered layer of rocks is called saprolite. Saprolite is a layer of broken bedrock pieces or fragments.
10. Direct students to place a 1 spoonful or 1 tablespoon of butterscotch chips in their cup. 

    

    This will be the saprolite layer.
11. Explain: The butterscotch chips represent the saprolite layer because they are smaller chunks than the bedrock layer but they are still pretty big chunks of rock.
12. Slide 8: The next layer is subsoil. Subsoil is made up of smaller rocks that have been weathered from the saprolite layer but this layer is also getting minerals and organic (living) material from the layer above it when water filters down.
13. Direct students to place a couple of spoonsful of pudding into the middle of their cup. NOTE: Make sure to instruct the students to put the pudding in the middle of the cup to avoid getting too much pudding on the sides of the cup. It makes it hard to see if too much pudding gets smeared on the sides of the cup. 

    

    This is the subsoil layer.
14. Slide 9: Now this is a very important layer. The next layer is the topsoil, or soil, which is a mixture of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things. This layer is a big mixture of things that come from plants, microbes, fungi, and even burrowing animals! Topsoil is a nutrient-rich layer of both organic material and of minerals from rocks. This is a good place for plants to root and other organisms to live.
15. Say: For our topsoil layer, we are going to use Oreo cookies. However, because topsoil has a mixture of stuff, including air, we need to crush up our “topsoil” layer before putting it into our cup.
16. Direct each student to place 2 Oreos into a plastic bag and have them crush the cookies with their palms, rolling pin or rubber mallet. Make sure they break up the small Oreo clumps with their fingers. Note: Have them reuse bags, crush them in advance, or some other alternative to save on plastic bags. 

    

    This will be the topsoil layer.
17. Explain: Soil is central to all life on land. Soil is a mixture of minerals, water, air, and organic matter (both dead and alive). Soil forms the surface of the Earth. So why is soil so important:

1. Soil helps plants grow.
2. Soil allows gas exchanges to happen between the land and air.
3. Soil provides habitat for most of the organisms on Earth.
4. Soil holds and cleans water.
5. Soil recycles nutrients.
6. Soil is used for building shelters and roads.

18. Direct students to add their crushed Oreo cookies to the top of the pudding or subsoil layer. 

    

    This is the topsoil layer.
19. Example that since soil is so important to life, we are going to use gummy worms to show all the living things that live in the soil.
20. Direct students to place one or two gummy worms into the cup under some of the Oreo layer.

    

21. Slide 10: The final layer at the surface is called the organic layer. This is an ideal place for plants to blossom and other organisms to live in and on.
22. Have students sprinkle shredded coconut on top of their Oreo/soil layer to represent growing plants. 

    

    Note: Many students do not like coconut so let them use it sparingly or on a small area of the surface.
23. Explain: This is an ideal place for plants to root and other organisms to live in and on.
24. Direct students to place the finishing touches with the lollipop tree and the gummy bear on top of the soil and shredded coconut “grass”. 

    

25. Go through the layers once more, asking students to point out the different layers in their cross section.
26. Have students fill out the Post-Assessment Worksheet.
27. Let student enjoy their critical zone cross section!
28. (optional) As they eat their cross section, discuss their cross section layers.

Vocabulary/Definitions

bedrock: Solid rock under looser surface material within the Earth's crust.

critical zone: The critical zone is the Earth's ever-changing skin. Here, air, water, animals, plants, soil, and rock interact.

organic layer: A layer of mostly dead plant leaves. This organic material gets mixed into the topsoil layer by plants and animals.

particle: A small object to which can be ascribed several physical or chemical properties such as volume, density, or mass.

saprolite: A layer with more rock fragments and fewer plant roots.

topsoil: A nutrient-rich layer of organic material and minerals. This is an ideal place for plants to root and other organisms to live.

Assessment

Pre-Activity Assessment

Brainstorming: In small groups, have students engage in open discussion. Remind them that no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas.

• What is rock?
• What is bedrock?
• How is soil created?
• Why is soil important?

Activity Embedded (Formative) Assessment

Hypothesize: Ask each group:

• What would happen if soil disappeared from the Earth?
• What would happen if all water disappeared from the Earth?
• What ways we can help the Earth?

Post-Activity (Summative) Assessment

• Students fill out the Post-Assessment Worksheet.
• (optional) Other question to discuss as a class:
• How do changes in climate and land-use affect ecosystems and water resources?

Troubleshooting Tips

Nuts should be avoided when purchasing food supplies.

Copyright

Contributors

Supporting Program

Acknowledgements

This curriculum was developed under National Science Foundation Network Cluster grant no. EAR 2012669 — Quantifying controls and feedbacks of dynamic storage on critical zone processes in western montane watersheds at the University of Colorado Boulder. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.