What Layers Are There?

Getting Down

Of course the answer to that question depends on your backyard. But unless your backyard is covered in concrete, Digger will probably find different types of soil. If he digs deep enough Digger might eventually hit solid rock. Do you know what it is called? (Hint: Think Flintstone^© town) The answer, of course, is bedrock.  But before Digger reaches the bedrock, he will have dug through three or four different layers of soil. These layers makeup what is called a soil profile. Each of the layers of soil is called horizons.

It's Tops!  

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: It is the organic material in the soil.

When Digger burrows his way past the topsoil, he will reach the subsoil. This soil horizon is usually lighter in color than the topsoil. The subsoil is often 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 mostly made up of clay or sand and has very little organic matter in it. Between the subsoil and the bedrock is a layer of small rocks that have started to break off from the bedrock. This layer of bedrock is called the parent material of the soil. This is the material that will eventually become the soil. The minerals in the parent material will determine the composition and the other characteristics of the soil. The bedrock layer is solid, uniform rock at the bottom of the profile.