This lesson will teach you about soil and why it’s important. We’ll explore what soil is, the different types of soil, and the layers of soil within Earth’s crust.
Soil Versus Dirt
Playing in soil can be so much fun! You can plant, dig, build castles, and even make mud pies out of it. Many people use the words ‘soil’ and ‘dirt’ to mean the same thing, but guess what? They’re actually two different things. You don’t play in dirt. Dirt is a substance that makes something dirty.
It’s what gets under your fingernails, on your clothes, or even trapped in the bottom of your sneakers after playing in soil. You get dirty while playing in soil!So what is soil? Soil is the upper layer of Earth’s surface that’s made of broken down rock combined with a mixture of living organic materials, like bacteria and fungi, and non-living organic materials. These non-living organic materials can include air, water, and broken down leaves and animals.
Why Is Soil Important?
Soil is important to most things that grow including, plants, animals, and humans. Let’s look at a few reasons why:
- Soil is needed for plants to grow.
- Soil keeps plants held into the ground.
- Soil releases carbon dioxide into the air, which plants need in order to grow and release oxygen into the air.
- Soil is home to many little organisms, such as insects and bacteria.
- Soil filters and helps to clean water.
What Lives in Soil?
As mentioned, you’ll find many living creatures within soil, and each creature has a special job to keep the soil healthy. Earthworms are particularly important, as they create tunnels through soil to allow air and water to reach the plants. They’re also considered decomposers, which means they break down the non-living plants and animals into very tiny pieces, called humus, so plants can absorb their nutrients.
Different Kinds Of Soil
The four main types of soils you will find throughout the world are sand, silt, clay, and loam.
- has the largest particles (pieces) compared to other types of soil
- feels rough
- doesn’t hold a lot of nutrients (food)
- provides great drainage for plants
- has medium-sized particles
- feels smooth
- dries into a light powder that can easily be wiped off
- holds nutrients and moisture well
- has the smallest sized particles
- is smooth when dry but very sticky when wet
- holds a lot of nutrients, but it doesn’t allow water and air to drain through
- doesn’t make the best environment for plants to live (but it’s fun to play with!)
- is a combination of the other three types of soil: sand, silt, and clay
- makes the best environment for plants to grow
The Layers of Soil
Get your shovels out and start digging. If you were to dig a hole very deep down into the ground, you would find many horizons, or layers, of soil.
- Organic matter (O) is a thick layer with grasses, twigs, and dead leaves.
- Topsoil (A) is a thin layer where most plants, trees, and organisms live and grow. It’s the only level you can grow plants and food.
- Subsoil (B) is made up of clay, iron, rock, and organic matter that have been broken down from the parent material level below.
- Parent material (C) is made up of large rocks. The parent rock breaks down slowly over years and eventually makes the subsoil and topsoil.
- Bedrock (R) is the bottom layer, made up of groups of large rocks. These break down slowly and eventually become the parent material horizon.
Soil is the upper layer of Earth’s surface and is made of broken down rock combined with living and non-living organic materials. There are four different types of soil and many different horizons below the ground.
Living organisms, such as earthworms, live in the soil and decompose the non-living materials to make nutrients within the soil.