- Soil is a mixture of weathered rock and organic matter that covers bedrock.
- Chemical weathering turns hard minerals into soft ones, while mechanical weathering breaks solid rock into smaller pieces.
- Plants and animals contribute organic materials through waste and dead organisms; decay of this organic matter produces acids that accelerate chemical weathering.
- Burrowing animals like earthworms, insects, and rodents help circulate air and water and mix mineral and organic remains.
- The material from which soil forms is called parent material. Soil that weathers directly from the bedrock beneath it is residual soil.
- Soil that does not match the bedrock it is over is transported soil, deposited by erosion agents like wind, rivers, or glaciers.
- A cross section of soil exposed by digging is called a soil profile, consisting of layers known as soil horizons: A-horizon (topsoil rich in humus), B-horizon (subsoil with transported minerals and clay), and C-horizon (partially weathered bedrock).
- Soil erosion is the removal of topsoil by running water or wind; it takes 100–400 years to form one centimeter of topsoil.
- Loss of topsoil can occur when plant roots are absent to hold soil, or due to salting roads, overgrazing, winds, construction, and mining.
Parent Tip: Review the logic above to help your child master the concept of soil profile worksheet.
