Soil Conservation: How Much of the Earth Is Usable Soil?

Humans depend on the soil for food, because it supports both plant and animal life. It may seem that soil is in abundant supply because we see it everywhere. What we do not often realize is that soil is not really that plentiful. The process of soil formation takes hundreds of thousands of years. Water and wind erosion are constantly depleting the amount of soil that is available for use. This activity will help you put into perspective how little of the Earth's crust contains usable soil.

Materials

Paper plate; Ruler; Scissors

Activity

1. Look at the paper plate and imagine that this paper plate represents a one-dimensional view of the surface of the Earth. As you read the statements below, use the scissors to cut away the parts of the Earth's surface that have unusable soil.
   1. Cut away three-fourths of the paper plate. This represents the fact that 75 percent of the Earth is water.
   2. Of the one-fourth remaining, half is composed of deserts, mountains, bogs, cities, and other areas that do not have usable soil. Cut away one-half of the slice that remains.
   3. Of the small slice you have left, 75 percent has temperatures and weather conditions that prevent it from being used for cultivation. Cut away threequarters of the remaining plate.
2. Look at the slice of paper plate you have left in your hand. It represents only about one thirty-second of the Earth's surface.

Follow-Up Questions

1. What are some ways that humans use the soil?
2. What are some ways that humans abuse the usable soil supply?

Answers

1. Answers will vary and could include farming and sites for building.
2. Answers will vary and could include bulldozing soil for construction and removing vegetation from soil, which increases the rate of erosion.

Extension

Do some research and look up the areas of the Earth that have the greatest amount of fertile soil. How are we trying to conserve the soil in these areas?