When you dig into the ground under the grass in your yard, you will find soil. But what Happens if you keep on digging? If you dug far enough, would you run out of soil? How far would you have to dig before you ran out? And what would you find there? If you dug far enough, you would hit solid rock. This is called bedrock. But before you got there you would have to dig through three different layers of soil. The layers are known as horizons, and all the layers together make up the soil profile. The first layer would be nothing but dark-colored organic materials. That is the layer formed by plantS and insects that have died and dead leaves that have fallen. Just under that is the topsoil. The topsoil is the best place for plants to take root and grow. It is a mixture of air, water, organic material (matter from dead plants and animals) and minerals (sand, clay, silt).

In most places the Topsoil is between six and 20 inches thick. The subsoil is the layer below the topsoil. It is made mostly of clay or sand and has very little organic material. Plants have a hard time growing in subsoil. Between the subsoil and the bedrock are a layer of sMall rocks that have started to break off the bedrock. This layer is the parent material of the soil. That’s because most of what makes up the soil was once part of the rock. Soil covers much of the land on Earth. It provides a substrate for plants (roots anchor in soil), a source of food for plants, and a home for many animals (insects, spiders, centipedes, worms, burrowing animals, bacteria, and many others). Soils are home to two or more tons of living things per acre. Microflora, insects, worms and animals, as well as other organismS, produce acids that, in turn, help break down soil minerals. Organic matter is beneficial to soils. It increases water-holding capacity, serves as a reservoir for plant nutrients such as nitrogen, and provides food for the living things in the soil.

Minerals have several different ways of getting into the soil. Sometimes they come from the ashes of volcanoes that have erupted. Usually the minerals come from rocks that have been broken apart. Water from rain flows into the cracks of rocks. When the water freezes, it expands and causes the cracks in the rocks to get bigger and little bits of rock break off. Sometimes the roots of trees and deep-rooted plants grow into the rocks and draw the minerals up through the roots and into the plant. The minerals become part of the leaves that later fall to the ground. Many rocks are broken apart by lichens — tiny plants that live on rocks. Sometimes water just keeps running over the rock until tiny particles start to wash away. We call all these processes “weathering.” Water and wind carry the tiny bits of rock along until they get trapped by the soil. It can take hundreds of years for rocks to break into pieces that are small enough to form soil. It takes between 200 and 500 years for just one inch of topsoil to form.