What is soil? It’s the unconsolidated mineral and organic matter that is on the immediate surface of the earth. Let’s break that down.
Unconsolidated means it is not solid, like a rock. Soil is loose; it can be dug up with a shovel and crumbled in our hands.
Minerals are non-living particles. Many of the minerals found in our soil came from rocks as they were weathered or broken down.
Organic matter comes from living things. It includes many micro-organisms. These are living things that are so incredibly tiny that they cannot be seen without a microscope. Organic matter also includes plants and animals that have died and are decomposing. This decaying plant and animal matter is called humus (pronounced hyoo-muhs).
Types of soil
If you dig deep enough, you will discover that there are different types of soil right on top of one another. Soil has distinct layers that look different and tell a story about the area. The layers are called horizons.
One area can have several horizons, but there are usually at least three: the topsoil, the subsoil and the parent soil. The topsoil has more organic matter from the decomposed living things, or humus, at the surface. The subsoil is almost always lighter in color and rich in minerals that come from the layers above. The parent soil rests just above the bedrock and contains minerals from the rock layer below it.
Words to know
Micro-organisms: Living things so small they cannot be seen without a microscope
Humus: The organic component of soil formed by the decomposition of plant material
There are many types of soil. It can have different colors, different smells and different textures. This makes sense if you consider that there are different types of bedrock and different living things in different areas.
No matter the type, all soil is important. Soil has many jobs that are important to the environment. Here are a few:
Soil as a home base and pharmacy: Soil provides the home base for all land plants. The roots spread and grow in the soil as well as anchor the plants in place, whether it is a dainty flower or a mighty tree. Soil also provides the nutrients that the roots need to absorb for the plant.
Soil as a sponge: When a plant uses carbon dioxide from the atmosphere, they pass the leftovers along to the soil. In this way, soil can absorb harmful greenhouse gases. The soil can hold onto these gases and keep our air cleaner than it would be without the absorbing power of soil. Soil can also soak up and hold water. If there is a lot of rain, water will just roll around on paved ground and can end up causing terrible floods, but soil can absorb the water and slowly release it.
Soil as a filter: Once water is absorbed by soil, soil actually cleans the water! Pollutants may get physically trapped by the soil. Chemicals in the soil may connect to and hold on to a pollutant, or biological micro-organisms may even change a pollutant into something less harmful.
Soils as a habitat: Soil provides an important habitat for many living things. Some animals, like robins, find their favorite hunting grounds searching for snacks in the soil. Mammals like woodchucks, moles and mice have underground tunnels throughout the soil that they live in. Snakes may steal an animal’s tunnel for a home of their own. Worms, insects and other bugs also like to make their homes in the soil.
Soil is awesome!
It may be strange to think about, but soil can be considered a living ecosystem. It grows and changes, and it needs air and water to stay healthy. When soil is dead and no longer doing the important jobs listed above, it is called dirt.
So as you play outside this summer, remember the soil beneath your feet is just as valuable as the growing plants and the wandering animals.
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