1. Soil is made up of rock particles (clay, silt, sand, and gravel), minerals, air, water, and organic matter (decayed organic material is called humus).
2. Loam is fertile, good for growing plants. The humus in loam provides nutrients and spaces for air and water--loam is about 25% air and 25% water. Also loam is about equal parts clay, sand, an silt, so the texture of the soil holds in a good amount of water. (Too much clay means too much water and too much sand means it doesn't hold in enough water.)
3. The soil horizons form in the order C, then A, then B. First bedrock is weathered to produce the C horizon (partially weathered rock). Then the C horizon is weathered and plants grow and contribute their parts to the soil which creates the A horizon (topsoil). Then particles from the A horizon (mostly clay and other rock particles) wash down and mix with the C horizon to make the B horizon (subsoil).
4. Humus is dark colored organic matter (made from plants and animals) that is found mostly in the topsoil. When remains of plants and animals decay due to activity of decomposes (like earthworms or bacteria) then humus is formed.r
5. Soil is mixed by organisms in the soil. Burrowing animals and earth worms can mix the soil.
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