How can I teach second and third graders that soil is an important and limited natural resource?
One of the challenges of teaching soil as a natural resource is helping young learners understand scale. Students can see soil almost everywhere around them, so the idea that productive soil and suitable farmland are limited may seem surprising.
An Earth as an Apple investigation gives students a concrete model they can watch change in front of them. As the apple becomes smaller during the demonstration, students explore how much of Earth is covered by water, why not all land is equally suitable for growing crops, and why healthy soil deserves protection.
This type of lesson works especially well in Grades 2–3 Earth science because it combines prediction, visual modeling, discussion, reading, and simple written reflection.
Start with a Simple Question: How Much of Earth Is Water?
Before showing students any numbers, ask them to predict:
How much of Earth do you think is covered by water?
Then ask:
How much do you think is land?
Students can color simple models or discuss their estimates with a partner before comparing their predictions with the actual proportions. The U.S. Geological Survey reports that approximately 71% of Earth’s surface is covered by water, leaving roughly 29% as land.
This creates a useful first surprise for young learners: even though we live on land, water covers much more of the planet.
In the resource, students first predict these proportions and then examine the difference between Earth’s water and land before beginning the apple demonstration.
Use an Apple as a Model of Earth
Next, introduce a whole apple and tell students:
Imagine this apple is planet Earth.
The whole apple represents Earth, while its outside surface helps students think about the limited surface area available on our planet.
Divide the apple into four approximately equal parts. Three sections can be used to represent water and one section to represent land.
At this point, it is important to explain that the apple is a simplified conceptual model, not an exact scale model. Three quarters equals 75%, rather than Earth’s actual approximately 71% water coverage. The goal is to help children visualize the much larger proportion of water compared with land, not to represent the percentages precisely. The Teacher Guide in the resource makes this distinction explicit.
Students can reinforce the idea by coloring three parts of their own apple model blue and one part green.
Help Students Discover That Not All Land Is the Same
The remaining land section leads to the next important question:
Can all land be used equally well for growing crops?
Students may initially assume that if an area is land, it can be farmed. Showing different environments helps challenge that idea.
For example, students can compare:
- mountains
- icy regions
- very dry land
- rocky land
- land that may flood
- towns and roads
- farmland
The key concept is not that crops are absolutely impossible in every challenging environment. Instead, students learn that some places are much easier and more suitable for farming than others.
This distinction is important for elementary science. Soil properties, water availability, slope, climate, drainage, and other environmental factors influence how well land can support plants and agriculture. USDA NRCS materials likewise describe soil depth, structure, water-holding capacity, nutrient availability, and other soil properties as factors related to productivity
Create the “Tiny Piece” Moment
As the demonstration continues, gradually trim the remaining land portion while discussing areas that may be difficult or unavailable for crop production.
Eventually, leave a very small piece.
This is often the most memorable part of the investigation.
Ask:
Why does this tiny piece matter?
Students can connect the small remaining piece with:
food → crops → farming
The purpose is not to claim that the final apple piece represents an exact percentage of global farmland. Instead, it serves as a visual reminder that productive land is limited and that people depend on suitable land and healthy soil to grow food.
The complete teacher sequence therefore includes an explicit reminder:
This is a conceptual model, not an exact percentage.
That note makes the model much stronger scientifically because students can benefit from the visual comparison without confusing it with a precise geographic calculation.
What Is Soil?
After the hands-on investigation, students are ready to move from the model to the science of soil itself.
At an elementary level, soil can be introduced as material at Earth’s land surface that includes mineral particles, organic material, water, and air.
The USDA Natural Resources Conservation Service describes soil as mineral or organic material at Earth’s surface that functions as a natural medium for plant growth. NRCS also emphasizes that soils develop through the interactions of parent material, climate, living organisms, landscape position, and time.
For Grades 2–3, these ideas can be simplified into four visual components:
rock particles + water + air + organic matter
The informational reading in the resource then connects these components with plant growth, food production, soil organisms, and farming.
Why Is Healthy Soil Important?
Soil does far more than simply hold plants upright.
USDA NRCS identifies several important soil functions, including supporting plant and animal life, cycling nutrients, regulating water, filtering pollutants, and providing physical support for roots.
For second and third graders, I would reduce these functions to three memorable ideas:
Plants Grow
Roots use soil for physical support while obtaining water and nutrients needed for growth.
Living Things Have Homes
Earthworms, insects, fungi, microorganisms, and many other organisms live in or interact with soil. Biological activity is an important part of a functioning soil system.
We Grow Food
Many foods begin with plants grown in soil. Healthy, productive soils therefore play an important role in agriculture and food production. NRCS emphasizes that maintaining productive soil is increasingly important as food-production demands continue.
These ideas are simple enough for elementary students while still representing real soil science.
Teach Soil Conservation with Actions Children Can Understand
Once students understand why soil matters, the natural next question is:
How can people protect it?
Keep this section concrete.
Keep Soil Covered
Plants and plant residues help protect soil from wind and water erosion. NRCS recommends maximizing soil cover as one of its core soil-health principles and explains that cover crops and other vegetation help reduce erosion.
For students:
plant cover → reduce erosion
Add Organic Matter
Compost and decomposing plant materials contribute organic matter to soil. Organic matter influences soil structure, nutrient cycling, water storage, and biological activity.
For students:
compost → return organic matter
Avoid Pollution
Healthy soil systems can filter and buffer some pollutants, but preventing contamination in the first place is an important part of caring for soil. NRCS identifies filtering and buffering pollutants as one of soil’s important functions.
For students:
avoid pollution → keep soil healthy
These three connections make an effective matching activity after the reading passage.
Add an Observation and Recording Sheet
A demonstration becomes much more meaningful when students have to record what they noticed.
After the apple investigation, ask students to draw:
At the start → After the cuts → At the end
Then use short reflection prompts:
What happened to the apple?
What surprised you?
Why is soil a limited resource?
These questions move students beyond simply watching the activity and ask them to explain the model in their own words.
For emerging writers, sentence starters work well:
I noticed that…
I was surprised that…
Soil is a limited resource because…
Finish with a Simple Exit Ticket
End the lesson by returning to the larger idea:
Why should people protect soil?
Students do not need a complicated answer.
Responses such as these show appropriate understanding:
- Soil helps plants grow.
- We need soil to grow food.
- Many living things depend on soil.
- Healthy soil is an important natural resource.
The resource finishes with both a short written response and a simple comprehension check, making it easy to see whether students understood the central concept
Why This Earth as an Apple Activity Works for Grades 2–3
Young learners often understand large Earth science ideas more easily when they can connect them to something familiar.
An apple gives students a concrete object they can:
- observe,
- compare,
- divide into parts,
- discuss,
- draw,
- and connect to a larger scientific idea.
The most important part is explaining that the apple is a model. It simplifies reality so students can visualize the concept. It is not intended to reproduce exact percentages of usable land.
That distinction also creates an opportunity to introduce an important science practice: models help us understand real systems, but models have limitations.
FAQ: Teaching Soil as a Natural Resource
Yes. The visual model, drawing, coloring, and short discussion questions are accessible to second graders. Teachers can read the informational passage aloud or complete it together as a class.
Yes. Third graders can go further by explaining why different types of land may be difficult to farm and by writing more detailed responses about soil conservation.
No. The apple is a conceptual classroom model. The initial three-parts-water/one-part-land representation is also approximate: USGS reports that about 71% of Earth’s surface is covered by water.
Soil supports plant growth, cycles nutrients, interacts with water, provides habitat for organisms, and supports food production.
At an elementary level, students can learn that maintaining plant cover helps reduce erosion, adding organic materials can support healthy soil, and preventing pollution helps protect soil systems.
soil • natural resource • crop • nutrient • organic matter • erosion • farmland
Professional References
For teachers who would like to explore the science behind this lesson, these are strong professional sources:
U.S. Geological Survey – How Much Water Is There on Earth?
Useful for the approximately 71% water / 29% land comparison.
USDA Natural Resources Conservation Service – What Is Soil?
Useful for soil definitions, soil functions, plant growth, water regulation, nutrient cycling, and pollutant filtering.
USDA Natural Resources Conservation Service – Soil Health
Explains soil-health principles including living roots, soil cover, reduced disturbance, biodiversity, water infiltration, and erosion reduction.
USDA Natural Resources Conservation Service – Role of Organic Matter
Useful background for teaching compost, organic matter, water-holding capacity, nutrient cycling, soil structure, and erosion.
USDA Natural Resources Conservation Service – Soil Facts
Provides soil-science definitions and background on soil-forming factors