Have you ever wondered how the age of soil is figured out? It seems like quite the guessing game to many and, in a lot of ways, it is.
Scientists that work with soil agree that different soils will form over time as the living organisms (the animals and plants living in the soil), parent material (the weathered rocks or items dropped by gravity, ice, water, or wind), topography (the landscape’s shape, and climate (the wind, rain, snow, temperature, etc) all interact.
Climate is well known to affect how fast that erosion and weathering happen, but it does not given very many clues as to how long the soil has been sitting in a particular place. The trees, parent materials, and landscape tend to give clues that are better so, when a scientist wants to know how old the soil is, they follow those clues.
Scientists that work with soil know that, in certain places in the landscape, soils will form faster than in other places. Flat landscapes in positions that are upland have more soil form than those in other places like on slopes. Because of erosion, slopes are limited on the rate soil forms. Also, in lowland areas, soil formation is slower because of deposits of new materials that hit the surface through gravity or floods. On top of that, we can look at the oldest tree growing in an area and know that the soil can’t be younger than it. It also can’t be older than the landscape materials it is found on. Geologists help the soil scientists to figure out the age of the landscape and which parent materials have been there the longest. Because the parent material deposits happened before we started writing down history, the geologists make a guess that is educated based on the landscape’s age and the materials it includes in relation to periods of known floods, volcanic activity, glaciation, and other events in history.
Pretty simple, right?