Tag: Information

How to Determine the Age of Soil

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.

2303526689_95b869a5bcClimate 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?

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Soil Colors

Have you ever paid attention to the different colors of soil? Well, they are colored by the materials and minerals that are found in them. Many of the colors we see are because of the oxides of iron. As an example, in the southern United States, there is a red tint to the soil in a lot of places because of hematite, an iron oxide mineral. Some soils will have a more brown color because of maghemite, an iron mineral; some are more yellow because of goethite, an iron oxide; some others will be a grayish green color because of hydromagnetite, an iron mineral.

soil-colourWith every color of the soil, the kind of iron oxide that is present is based on the soil’s conditions when the oxide was formed, such as potential organic matter, water content, and the temperature. Hot soils help hematite to form when there is a lot of oxygen present. When small amounts of oxygen are present because the soil is often saturated, hydromagnetite is formed.

There are other materials within soil that can cause colors that we see. Different salts in the soil can cause it to have a white crust. These salts are found naturally in some soil environments. High levels of organic materials that are partially decomposed can cause some top soils to have a black color.

Color is a powerful tool that is used by the soil scientists to help them understand the formation of different types of soil since the color is determined by the conditions the soil is formed under. It gives very good hints to the scientists that are studying it.

Many people wonder how iron effects our ability to grow crops and other things in the soil. The iron is actually a very small part of what makes up the soil, so it doesn’t influence it a lot. You can think of it like the paint in a home. The paint makes up a very small part of the home itself, but it can influence how the home appears. This is the same way iron oxide is in the soil. It pretty much just determines how it looks.


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The Properties of Soil

Have you ever asked yourself what soil is made of? Well, it’s made of different types and sizes of solid particles. Some of those are organic while others are minerals. The spaces between the particles can be filled with water or air.


Over time, the soil’s mineral particles begin to change due to weathering. Many things weather rocks, such as hot and cold weather, plant roots, ice, and water. Size is the only thing that changes through this physical weathering process. On the other hand, chemical weathering can change minerals or rocks into other minerals or rocks. They become something completely different. Here is one way to think about it: Take a cookie and break it in two. Each piece is still the same cookie but smaller. You can break it over and over again, and it’s still the cookie. That is just like physical weathering. Put the cookie in your mouth, though, and the saliva begins to mix with the cookie. This will begin the process of digestion. Once this happens, the cookie is no longer a cookie. You couldn’t put it back together again. This is like chemical weathering.

Another part of the soil is humus. Organic particles in the soil make up humus. The organic particles are decomposed parts of animals, plants, and microorganisms. The soil “eats” the organic tissues from the plants and animals. The soil gets energy from these and then will create waste. Humus is the waste product that is produced from the soil.

thumb-ebf72f9951b04c5d05330f906135c161The particles in the soil are separated by their size. If a particle is over two millimeters, it is gravel. If it is between 2 and 0.05 millimeters, it is considered sand. Silts are between 0.05 and 0.002 millimeters. If the particles are under 0.002 millimeters, they are clay. The ratio of mixture of these particles determines the texture of the soil. Clumps (peds) are formed when the individual particles are held together by humus. The soil structure is determined by the size and shape of the peds.

As you can see, air, water, organic solids, and minerals make up soil. The properties of the soil are affected by the microorganisms, animals, and plants that live in the soil.






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