- 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 material produces acids that speed up chemical weathering.
- Burrowing animals like earthworms, insects, and rodents help mix soil components and circulate air and water.
- The material from which soil forms is called parent material; soil formed directly from underlying bedrock is residual soil.
- Transported soil does not match the bedrock beneath it and was deposited by erosion agents like wind, rivers, or glaciers.
- A cross section of soil is called a soil profile, composed 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 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; salting roads, overgrazing, winds, construction, and mining can all reduce plant cover.
Parent Tip: Review the logic above to help your child master the concept of weathering and soil formation worksheet.
