Soil Age

The weathering forces, as influenced by the five soil-forming factors, result in the formation of soil from rocks and parent materials. However, the soil formed is not just a loose unconsolidated, disorganized mass of various size particles. The soil has definite organized qualitative and quantitative characteristics reflecting the forces from which it was formed.

The age of most persons are measured in years since birth. For people and soils, there are also ways to judge age in terms of “maturity”. The age of a soil is determined by the amount of weathering that has occurred; that is, to what extent the parent material has been converted to distinct horizons or soil layers. Soil age is based on three general criteria:

• The more horizons that are present, the older the soil.
• The thicker the horizons, the older the soil.
• The more difference there is between adjacent horizons, the older the soil.

Soil age is not an exact measure. It is usually described simply as young, mature or old. A young soil has a thin A horizon and often no B horizon. A mature soil has A and B horizons of average thickness which show some differences from each other. An old soil shows thick horizons which are very different from each other. Horizons are described in more detail in the following section.