What Is Soil?

Contributor: Hannah Brooks. Lesson ID: 12446

"Dirt" seems like such a dirty word: dirty dishes, dirty clothes, dirty windows. But it comes from a good home: soil! What's the difference? Dig into this lesson and see how important and alive it is!

categories

Earth Science

subject
Science
learning style
Visual
personality style
Lion
Grade Level
Intermediate (3-5)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

Audio:

Have you ever thought much about dirt, other than when you track it into the house? What is dirt? You need it, but not under your fingernails!

Have you ever played in the dirt?

It can be a lot of fun, but also pretty messy. Scientists use another name for dirt in the ground: soil.

soil

How is soil different from dirt? Well, soil is made up of things like minerals, organisms, water, and other matter, like leaves and roots. It is able to support living things like plants and animals. Dirt has been removed from the Earth and is not able to support life. While many people use "dirt" as another word for "soil," it is actually different.

Can you list some ways that humans rely on soil? Write these down on a sheet of paper, and consider adding more as you move through the lesson.

We plant plants in the soil. These plants provide oxygen that allows humans and animals to breathe and provides crops that we can eat.

farm

These plants take in the carbon dioxide we breathe out, and release oxygen. Soil helps to clean the air by working with plants to absorb gases and waste products. Soil also plays a role in the water cycle. Water enters the soil as rainfall or runoff, and is cleaned as it soaks down through different soil layers. To learn more about the water cycle, visit the Elephango lesson found in the right-hand sidebar under Additional Resources.

water cycle

As the water moves through the soil, it helps other nutrients move. Plants and organisms need nutrients like carbon, nitrogen, and phosphorus in order to survive. The soil under your feet is home to many different types of organisms. There are bacteria that break down dead leaves, earthworms that mix the soil up, and plants that use the soil as a place to grow roots. Soil contains a special ecosystem, or group of living organisms working in an environment.

soil food web

Did you know that we use soil in so many ways? Which use of soil do you think is most important? Write a two-sentence reflection to answer that question.


Soil is organized into layers, or horizons. These horizons combine to create a soil profile. The soil profile is kind of like a record. It helps us know where and how the soil formed.

soil layers

The top layer is called the O horizon, because it contains a lot of dead organic matter that is being broken down. This is the youngest layer, and can be thick or thin depending on where the soil is located.

leaves

Under the O horizon is the topsoil, or the A horizon. Here, the nutrients from the organic matter combine with minerals in the soil to create a rich substance perfect for growing plants!

Topsoil is usually a dark brown, similar to potting soil!

potting soil

Under the topsoil is subsoil, or the B horizon. In this layer, we have lots of minerals, because they have been picked up by water as it moves through the upper layers. The process of water drawing minerals downward is called leaching.

The subsoil sits on the parent material. This is the original material that started becoming soil as the rock was weathered away. The parent material determines which minerals we will find in high amounts in the soil. This is also known as the C horizon.

C horizon

All soil has layers, but not all soils have each layer clearly separated. It may be hard to identify the soil horizons in your own backyard, because they often blend together. The nutrient-rich topsoil helps us grow crops and plants that we can use for many purposes. The B horizon provides a place for minerals to be stored, resting above the parent material in the C horizon.

Draw a quick sketch of a soil profile and include labels. Share with a parent or teacher before moving to the Got It? section, where you will learn more about how important soil is in our world.

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