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The Earth’s Soil

Walking through a forest, you’ll see life everywhere. Huge trees, all types of animals, and stranger things like fungi all live in one ecosystem! And what allows for this great diversity? Something very ordinary: soil! The Earth’s soil is a rich mixture of nutrients, water, and sediment which is central to life on our planet.An image of a farmer holding a handful of rich dark dirt.

What is The Earth’s Soil? (Soil Ingredients)

The first thing we need to know about soil is its make-up. Soil contains a lot of different things; some people call it its own ecosystem! Still, we can point out a few essential ingredients:
  1. Sediment – Every soil contains some mixture of sediments. This determines a soil’s type. The three main sediments are sand, silt, and clay. Ideal soils (for farming) are a mixture of the three.
  1. Organic Matter – Soil contains a lot of partially decomposed organisms. We call this organic matter. Microbes in the soil break it down to make important nutrients. Most organic matter comes from plants.
  1. Minerals – There are tons of different minerals in the soil. They’re used by plants for growth. When plants die, their minerals return to the Earth.
  1. Water – Soils contain a great deal of water, though some more than others. A soil’s type and what biome it’s in determines how much. 

    An image of a muddy child and dog in a river.

    Flowing water can saturate the soil, giving it a muddy texture. This is especially common in wetlands.

Where is Soil Found?

Soil exists throughout the world and in nearly every biome. Even so, there a few requirements for its formation. We don’t find much of it, say, on top of mountains or in deserts. That’s no coincidence.
For one, soil can’t form where there’s a lot of erosion going on. Soil formation is a very slow process. Components layer over one another slowly and in a precise order. They thus have to be relatively undisturbed. In places with extreme winds (again, mountains and deserts), they might not be able to form.

That being said, weathering and erosion are still important to soil formation. Generally, soils don’t form in very dry places because not enough soil ingredients get deposited there. What’s more, they don’t form very high up. There are two primary reasons for this. 1) Too much weathering goes on, removing essential sediments and 2) There’s no way for soil ingredients to climb far upwards.

An image of the Banff Mountains

Notice how grassy soils gradually stop-off as they move up the mountain.

How is Soil Formed?

Soil formation is a very long, yet simple process. It relies on the gradual weathering of rock to produce sediments. As we go deeper into the layers of the soil, we actually go from sediment to stone to bedrock. Soil forms the opposite way. First, bedrock goes through erosion to produce a layer of large stones called regolith (also known as parent rock).

Parent rock is then weathered even further. At this point, insects might burrow into it and break it up. Or, perhaps, acid rain crumbles the rock into sediment. In any event, gradual breakdown of the parent rock gives us our third layer: the subsoil. Subsoil is the first layer that you might actually think of as ‘soil.’ Some plants might even grow their roots into it.

An image of an ant hill.

Ants might ruin your picnic. But, they probably helped make the soil your food was grown in!

As they do, they start a process called nutrient cycling. This makes the soil richer and further alters its composition. If it goes on for a while, we might get our topsoil, a nutrient-rich layer. Finally, as plants start to die and decay, they’ll form the uppermost soil layer. We call this layer the organic matter, and it’s where most decomposition occurs.

Layers of Soil

The five layers we discussed above each have unique properties. We’ll discuss them only briefly in this article. But, if you’re interested, you can read more about them here.
  1. Organic Matter – The layer of soil full of plant parts, hungry organisms, and decomposing things.
  1. Topsoil – A layer with slightly less organic matter and more sediment. Its saturated with plant roots, looking for nutrients.
  1. Subsoil – A layer which collects (or leaches) materials from the topsoil. It’s a thieving layer!
  1. Parent Material – The stony layer which contributes sediment to those above.
  1. Bedrock – The beginning of the Earth’s crust.

    An illustration of the layers of the Earth's Soil.

    The different layers of the soil.

Difference Between Soil and Dirt

The difference between these two things isn’t huge. That said, it’s an important one. Dirt is soil that’s separated from its original soil layer. It’s not receiving any new nutrients, so it just becomes a light brown dust. We ought to protect our soil so it doesn’t become like that!

An image of nutrient depleted dirt.

Dry dirt is nothing like rich soil.

Other Great Resources

An Entire Website on Soil: https://www.soils4kids.org/

Ducksters Earth Science: https://www.ducksters.com/science/earth_science/soil_science.php

(Video) Introduction to Soil: https://www.youtube.com/watch?v=I3A7OnTLSM8


Written by: Noah Louis-Ferdinand