Soil is formed from weathered rock and organic matter over long periods of time. It is composed of mineral particles from parent rock along with decayed plant and animal remains. Soil formation involves interactions between air, water, plants, animals, rocks, and chemicals that break down rock into smaller pieces that are mixed into the soil layer. Soil has a profile of distinct horizontal layers called horizons including topsoil, subsoil, and underlying bedrock that vary in composition and provide habitat for plant roots and microbes.