When you think of soil you think about dirt, right? In theory, soil is only what you find under your feet and dirt is what you find under your finger nails. However, soil actually has more depth and characteristics than that. It is the accumulation of loose, weathered material that covers much of the land surface of Earth.  Soil varies in depth, composition, age, color, and texture. Although its chief component is weathered rock, a true soil also contains water, air, bacteria, and decayed plant and animal materials (humus). The rock from which a soil forms is called the parent material. Soil that forms directly from the bedrock beneath it is residual soil.
    If the soil forms from material that was transported to the location by erosion, it is transported soil. Soil is the organic remains of decomposed vegetation. In agricultural soil, it is the medium that supports crop plants, both physically and biologically. Soil may be from a few inches to several feet thick. The inorganic fraction of soil may include various sizes and shapes of rocks and minerals, in order of increasing size. These are clay, silt, sand, gravel, and stone. Coarser soils have lower capacity to absorb organic plant nutrients, gases, and water, which are important for plants. Soils tend to absorb substances, so therefore they are usually better suited for agriculture.