Soil scientists have identified over 70,000 kinds of soil in the United States. Soil is formed from rocks and decaying plants and animals. Different-sized mineral particles, such as sand, silt, and clay, give soil its texture. Fungi and bacteria help break down organic matter in the soil. Plant roots and lichens break up rocks which become part of new soil.
Roots loosen the soil, allowing oxygen to penetrate.
This benefits animals living in the soil. Roots hold soil together and help prevent erosion. Five to 10 tons of animal life can live in an acre of soil. Earthworms digest organic matter, recycle nutrients, and make the surface soil richer. Mice take seeds and other plant materials into underground burrows, where this material eventually decays and becomes part of the soil.