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Earth Science for Kids
What is soil?
Soil is the loose upper layer of the Earth's surface where plants
grow. Soil consists of a mix of organic material (decayed plants and animals) and broken bits of rocks and minerals.
How is soil formed?
Soil is formed over a long period of time by a number of factors. It can take up to 1000 years for just an inch of soil to form. Besides time, other factors that help soil to form include:
Why is soil important?
- Living organisms - This includes organisms such as plants, fungi, animals, and bacteria.
- Topography - This is the relief or slope of the surface of land where the soil is forming.
- Climate - The overall climate and weather where the soil is forming.
- Parent material - The parent material is the minerals and rocks that are slowly disintegrating to form the soil.
At first you may think of soil as just dirt. Something you want to get rid of. However, soil plays a very important role in supporting life on Earth.
Properties of Soil
- Plants - Many plants need soil to grow. Plants use soil not only for nutrients, but also as a way to anchor themselves into the ground using their roots.
- Atmosphere - Soil impacts our atmosphere releasing gasses such as carbon dioxide into the air.
- Living organisms - Many animals, fungi, and bacteria rely on soil as a place to live.
- Nutrient cycles - The soil plants an important role in cycling nutrients including the carbon and nitrogen cycles.
- Water - The soil helps to filter and clean our water.
Soil is often described using several characteristics including texture, structure, density, temperature, color, consistency, and porosity. One of the most important properties of soil is the texture. Texture is a measure of whether the soil is more like sand, silt, or clay. The more like sand a soil is the less water it can hold. On the other hand, the more like clay a soil is, the more water it can hold.
Soil is made up of many layers. These layers are often called horizons. Depending on the type of soil there may be several layers. There are three main horizons (called A, B, and C) which are present in all soil.
Interesting Facts about Soil Science
- Organic - The organic layer (also called the humus layer) is a thick layer of plant remains such as leaves and twigs.
- Topsoil - Topsoil is considered the "A" horizon. It is a fairly thin layer (5 to 10 inches thick) composed of organic matter and minerals. This layer is the primary layer where plants and organisms live.
- Subsoil - Subsoil is considered the "B" horizon. This layer is made primarily of clay, iron, and organic matter which accumulated through a process called illuviation.
- Parent material - The parent material layer is considered the "C" horizon. This layer is called the parent material because the upper layers developed from this layer. It is made up mostly of large rocks.
- Bedrock - The bottom layer is several feet below the surface. The bedrock is made up of a large solid mass of rock.
- The process by which minerals move down through soil is called leaching.
- In a teaspoon of good soil there will typically be several hundred million bacteria.
- The average acre of good cropland will be home to over 1 million earthworms.
- Soil is mostly made of the elements oxygen, silicon, aluminum, iron, and carbon.
- It is possible to over-farm soil and remove so much of its nutrients and organic matter that plants will no longer be able to grow in it.
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