Table Of Contents

Soil Composition.....................................................................Page 4

Soil Horizons............................................................................Page 6

Chemical Weathering VS. Mechanical Weathering.............Page 8

The Dust Bowl........................................................................Page 10

Importance Of Soil................................................................Page 12

Glossary/Key Terms..................................................................Page 14

Soil Composition

Soil is a mixture of rock particles, minerals, decayed organic material, minerals, water and air. Most of the rock particles are from sand, silt, and clay. The organic material is also called humus and is from decayed dead plants or animals.

Composition Chart

Soil Horizons

Soil has layers. These layers are called soil horizons. There are three soil horizons. Soil horizon A, B, and C. Horizon A is made of top soil, a crumbly, dark brown soil that is a mixture of humus, clay, and other minerals. Most minerals from the top soil get washed down (not much humus, though)to the B Horizon, making sub soil. The C Horizon is made from partly weathered and eroded rock from elsewhere. Each soil horizon is different because they have different composition, age, and texture.

Soil Horizon Diagram

Chemical Weathering VS. Mechanical Weathering

Mechanical Weathering is the process when rock is physically broken down into smaller pieces, like ice wedging. Chemical weathering uses chemical changes to break down rocks, like with acid rain. They are different because mechanical weathering uses physical changes to break down rocks while chemical weathering uses chemical changes to break down rocks.

Mechanical Weathering Example

Chemical Weathering Example