Here is an activity you can do when you are somewhere where there is a section of soil to look at, or if you want to dig a deep pit in a garden with your parents. (Choose somewhere under a lawn, not a flower bed where the soil has been dug over recently.)

Look at the top of the soil and feel the material near the surface. It should be dark and slightly slimy when wet. The sliminess is the rotted plant materials from plants that have died. The rotted material has been dragged underground by worms.

Now look half a metre or more down and feel the soil again. It should be more sticky or sandy, but it will not be slimy because there is no rotted material down here.