Soil Horizons

Dirt is what you get under your fingernails.  Soil is where plants grow.  And the more you know about soil the more you’ll understand that there isn’t any part of this world that isn’t wondrous.

In the Field

Go outside with a shovel and dig a big hole straight down.  Kids love to dig in dirt . . . oops, soil, so let everybody dig their own hole.  Look at the layers the soil forms into.

This photo is of the bank on the side of a road. The layers of soil have been exposed. Photo by Famartin, CC license, Wikimedia.

The top layer usually is dark brown, or even black looking.  It gets this color because there’s lots of organic stuff decomposing in it, stuff like leaves, dead ants, and roots.   The next layer still has quite a bit of organic stuff, but it’s not so dark.  Then you get down to the sub-soil, where there is very little organic matter at all, instead the soil is made up of lots of itty bitty pieces of rock and clay with some bigger rocks sort of floating around in there.  Below that is the layer where the rocks are getting bigger and the spaces between them fewer.  Finally you reach bedrock, the solid chunks of boulders and rock that make up the continental plate.

Soil Horizons

Each of these layers is called a horizon and they are labeled with letters: O, A, B, C, and D, with O being the top organic layer and D being the bedrock.  When you dig your hole outside, you may or may not see all these layers, but you will certainly see some.  Try to identify them.  Then draw and label the horizons you see in your soil.  Compare it the “ideal” soil horizon picture.

Image by the PD-USGov-USDA, public domain.

Printable Soil Horizons Worksheet

You can print out a Soil Horizons Worksheet to color and label yourself.

This is a lesson and printable worksheet on soil horizons.  Perfect for when studying earth science.

Additional Layers

  • Which layer of soil do you think is best for plants?  Design an experiment to find out.
  • Measure the depth of each layer that you found.
  • You know the old saying . . . “Dig a hole to China”, well if you could dig straight through the Earth, where would you end up?  Use a globe to figure it out.
  • Read A Hole Is To Dig by Ruth Krauss or Holes by Louis Sachar.
  • Write a scientific detailed description of the hole you dug for your writer’s notebook.

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