How Is Soil Formed?

There are four basic "ingredients" that go into the "recipe" for making soil: tiny pieces of rock, decayed plants and animals, water, and air.

When small pieces of rock break off larger ones, they form the basis of all soil. This breaking can occur in several ways: through the action of glaciers pushing rocks along the ground and grinding them against other rocks; through the action of chemicals in water eating away at rocks; through changes in temperature causing water to freeze in rocks and crack them open; through the force of wind throwing sand and pebbles against rocks; and through the movement of plant roots splitting rocks apart. This rocky, ground-up material is called the parent material of the soil.

When a plant or animal dies, its remains are attacked by bacteria which decompose, or break them down. This decaying matter combines with the parent material and provides the soil with many nutrients to help new plants grow.

Water and air fill in the spaces between the ground-up rock and decaying matter to provide places for tiny insects to live and for plant roots to grow.