Objective:Explain what soil consists ofDescribe the horizons of soil

Essential Question: Why do soil horizons form the way they do?

Earth’s Surface Text 4.2

How does soil form?It takes a long time for soil to form. Soil forms as rock is broken down by weathering and mixes with other materials on the surface. Soil is constantly being formed every time bedrock is exposed. Over time, soil develops layers. We call these layers horizons.

Horizon 0 Horizons A B C

R Bedrock

Horizon 0

• Thin surface• Made of organic material(dead leaves, plants, &

grass)

Horizon A• Horizon A is made up of topsoil. Topsoil is a

crumbly, dark brown soil that is a mixture of humus, clay, organic matter, and other minerals.

Horizon B

The B horizon is called subsoil. Subsoil consists of clay and other particles that have washed down from horizon A. Usually a brownish-red color.

Horizon CThe first soil horizon to form from the weathering of bedrock is the C horizon. The C horizon contains only partly weathered rocks. Rock is usually a light yellowish brown color. Below the C horizon is where

you will find bedrock.

Bedrock

• Deepest layer, soil and unweathered rock.Grayish-light brown color

Soil HorizonsFoldable—1)Color your “Horizon”2) Cut to make flip book and GLUE in ISN3) Write the definition for each horizon using this PPT and your textbook.

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