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What Layers Are There?

Think about this: you have a dog named Digger who has his name for a reason. Digger really likes to dig. All day long when you are at school, he digs. As Digger goes about digging, what will he find (besides the bones he buried the last time you had pork chops for dinner)?
Of course, the answer to that question depends on your backyard. Unless your backyard is covered in concrete, Digger finds different types of soil. He digs through three or four different layers of soil. Each layer of soil is called a horizon. All the layers (horizons) makeup what is called a soil profile.


The first layer of soil (the first horizon) is usually darker. What do you think causes this layer to be darker?

A. The sun tanning the surface of the soil?
B. The inorganic materials in the soil?
C. Leftover volcanic debris?
D. The organic material in the soil?

Answer: D The organic material in the soil.

The first horizon, or layer, is darker in color. Often it is blackish because it is mostly made of organic matter. This horizon is also called the topsoil. Utah has less organic matter than other places in the United States due to the lack of precipitation and plant life. In areas with more moisture and vegetation, you find that the layer of topsoil goes much deeper than in Utah.
When Digger burrows his way past the topsoil, he will reach the subsoil. This soil horizon is lighter in color than the topsoil. The subsoil is brownish and less productive than the topsoil. Minerals in the subsoil are not in a form that is easy for plants to use. The subsoil is made up of clay or sand, and contains very little organic matter.
Between the subsoil and the bedrock is a layer of small rocks that start to break off from the bedrock. This layer of bedrock is called the parent material of the soil. This is the material that becomes the soil. The minerals in the parent material determine the composition and characteristics of the soil.
Using the information above, make a "Soil Profile" poster or model. Be sure to label each horizon. You may want to make an edible model of a soil profile. Hint: Do not use the real stuff (dirt) for this project. The whole point is to enjoy devouring the project when you finish. So use your imagination here. Think in terms of your favorite food. Hey, you can even take gelatin and make a pretty good soil profile. Think about it!

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Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 4th grade science core.

Updated October 24, 2008 by: Glen Westbroek

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