Merrill Earth Science

Weathering and Soil

5-1 Weathering

Weathering: is the term used to describe the breaking of rocks into smaller fragments.

Two types:

1. Mechanical or Physical Weathering: is weathering that breaks apart rocks without changing their chemical composition.

Examples: rocks rolling and breaking, roots breaking rock, Ice wedging-water freezes in cracks, expands, and forces the rocks apart.

2. Chemical Weathering: occurs when substances like water or gases in the air react with the minerals in rocks and changes the chemical composition of the rocks.

Examples: Water dissolves minerals and carries them away, thus changing the composition of the rock.

Rusting (oxidation-when oxygen combines with minerals in the rock such as iron.)

Plant acids- change the composition of rocks and thus weathers them

Climate is important in weathering. The more moist the climate is the faster weathering occurs.

5-2 Soil

Soil forms when organic material is slowly added to weathered rock particles.

Soil: is a mixture of weathered rock and organic matter. The more organic material (humus) is in the soil the more fertile it is.

Soil Profile: See the horizons in figure 5-8 on page 131

5-3 Soil Loss

Poor Farming practices-

Desertification-

Deforestation-