If the World Were an Apple
Objectives
The point of this lesson is to teach students to learn the importance of topsoil, the amount of topsoil we have, and why we should care for it.
The two big questions this lesson will answer are:
Why is topsoil important in our world?
How does healthy topsoil affect our lives?
STEAM Connections & Kentucky Academic Standards
NGSS
Earth Systems: Earth Materials, Role of Water, Human Impact & Sustainability - K-PS3-1, 4-ESS2-1, 4-ESS2-2, 4-ESS3-2, 5-ESS3-1
Math
Numbers & Operations: Fractions
ELA
Writing & Research
Introduction
Worldwide, 25 billion tons of agricultural topsoil are swept away every year—that’s 7 percent of the world’s good growing land every decade. In these activities students will come to appreciate how little topsoil there is in the world and how it can easily be lost through erosion. In the garden, students will discover techniques to build soil health and protect soil from erosion and determine the ability of soil to support the growth of many plants, including those important to our food supply. Learn more at kyreadysetgrow.org.
Vocabulary Focus
Topsoil: Top layer of soil
Erosion: When soil or rocks are moved from one place to another by water and wind
Materials
For the teacher: apple and a sharp knife
Procedures
Say, “All around the world, topsoil is being swept away every year by erosion. Topsoil is the top layer of soil that has important nutrients. Erosion occurs when water and wind wear away soil.”
Write both of the above vocabulary words, with definitions, on the board. Say, “Topsoil is essential because we need it to grow crops and plants so we can eat. Erosion can take away the topsoil that we need.”
Ask the students the following discussion questions: What else do you know about soil? What is it? Why do you think plants need it? How does it help humans?
Say, “During this activity I want you to think of the world as this apple. I am going to cut it into smaller parts to show you how much topsoil there is on Earth.”
Begin the “If the Earth Were an Apple” activity. Show the students the apple and give the following demonstration:
Let’s say this apple is the Earth. That is called a representation or model.
Cut the apple into quarters and set three of the quarters aside.
Three quarters of this apple represent all the oceans on Earth. The remaining quarter represents all the land on Earth.
Cut the remaining quarter in half and set one piece aside.
One half of the land is unfit for humans and plants; it is either too hot, like a desert, or too cold, like the north and south poles.
Cut the remaining piece into four pieces and set three aside.
Of the land that humans can live on, only this small piece is land that we can grow food on. The rest is forested, too rocky, too wet, or there isn’t enough sun for plants to grow.
Peel the remaining piece.
This thin peel represents the thickness of the soil in which we grow our food. It is only about three feet deep. This tiny portion is the only area out of the whole Earth where all the right conditions exist to grow food crops. Enough food has to be produced on this small bit of land to feed ALL of the people on Earth.
Options Outside Excursion - Erosion
Estimated Time: 10 minutes
To observe places where erosion has occurred. I generally walk students around the schoolyard. We look at areas around downspouts, drains, around roots of trees, etc.
Engage students in a discussion regarding what could happen if nothing was done to stop the erosion. Ask if they think we as a class could do anything to help solve this problem in our school yard.
Examples my students came up with: We had a downspout at the corner of our building next to the outdoor classroom. The run-off water had eroded the soil completely and a ditch had formed. Student solution: Add a piece of gutter to divert the water into a rain barrel. Next, to fix the problem, add topsoil to the eroded area and plant a small shrub there.
A big question, and an entire unit, is, What can people do to stop or slow down erosion?
Then ask students to tour their yard at home and see if they can find any areas where erosion has occurred. The next day, ask how many did that and if they found any areas. Let students share. Ask if they can think of anything they or their families could do to solve this problem at their home.
Review/Journaling Assessment
Write an Argument: Why is topsoil important in our world? (Possible answers: We use topsoil to grow food and plants; plants convert carbon dioxide into oxygen for us to breathe.)
Write and Informative/Explanatory Text: How does healthy topsoil affect our lives? (Answer: Without healthy topsoil we would not be able to grow food to eat.)
Write and Informative/Explanatory Text: How can erosion be prevented? (Possible answers: Keeping soil covered with plants, mulches or other covers; diverting water, reducing use of bare ground.)
Math Connection
Grades 3+
Following the demonstration, ask students to use a piece of paper to represent the surface of the Earth. They may draw or cut out sections that represent:
Water - 3/4
Land - 1/4
Deserts/Arctic Poles - 1/8
Forests - 1/16
Marginal Land - 1/32
Cropland - 1/32 but only thin layer of topsoil