Weathering and Soil Information

The Effects of Weathering All exposed rock is in the path of weathering and erosion. Weathering is the process that breaks down rock and other substances at the Earth’s surface. Heat, cold, water, ice, carbon dioxide, oxygen etc.. all contribute to weathering.

Weathering and Erosion Weathering examples: Repeated freezing and thawing. Rainwater dissolving minerals. Erosion is the movement of rock particles by wind water, ice, or gravity. Weathering and erosion work together to carry away the rocks at the surface. There are two types of weathering: Mechanical Weathering Chemical Weathering

Mechanical Weathering Mechanical Weathering: rock is physically broken into smaller pieces that have the same chemical composition as the rock they came from. Examples: freezing and thawing, release of pressure, growth of plants, actions of animals, and abrasion (grinding away of rock by particles in the wind and water).

Chemical Weathering Chemical Weathering: the process that breaks down rock through chemical changes and produces rock particles that have a different mineral makeup from the rock they came from. Examples: Hot or soft spots in rock Water Oxygen Carbon Dioxide Living organisms Acid Rain

Rate of Weathering The most important factors that determine the rate at which weathering occurs are the type of rock and climate . Type of Rock Minerals will determine the rate. Permeable rocks (full of tiny air spaces) weather faster. Climate: Weathering occurs faster in wet climates and higher temperatures.

Soil Formation Over many years, weathering and erosion will cause the formation of soil. Soil is the loose, weathered material on the Earth’s surface in which plants can grow. Soil forms as rock is broken down by weathering and mixes with other materials on the surface.

Soil Composition Soil is constantly being formed wherever bedrock is exposed. Bedrock is the solid layer of rock beneath the soil. Soil is a mixture of rock particles, minerals, decayed organic material, air, and water.

Soil Composition and Texture The decayed organic material in the soil is humus. Humus is a dark-colored substance that forms as plant and animal remains decay. Soil texture depends on the size of individual soil particles. Soil texture is important for plant growth.

Soil Horizons A soil horizon is a layer of soil that differs in color and texture from the layers above or below it. Topsoil (A horizon) is a crumbly, dark brown soil that is a mixture of humus, clay, and other materials. Subsoil (B horizon) usually consists of clay, and other particles washed down from the topsoil, but little humus. C horizon contains only partly weathered rock. The rate at which soil forms depends on the climate and type of rock.

Life in Soil Some organisms mix the soil and make spaces in it for air and water. Other soil organisms make humus, the material that makes soil fertile. Humus forms through decomposition. Fertile soil is rich in nutrients that plants need. As plants shed leaves, they form a loose layer called litter.

With and Without Worms 