What 2 layers make up the topsoil?

Horizon O and horizon A make up topsoil.

What layer is made up of partly weathered rock?

Horizon C is composed of partly weathered rock.

How does material move from horizon A to horizon B?

The process of leaching moves material from horizon A to horizon B.

What do horizon A and horizon B have in common?

Both horizon A and horizon B have decayed organic material called

humus.

Where does the material in horizon C come from?

The partly weathered rock in horizon C comes from unweathered parent rock.

What is the composition of horizon O?

Horizon O is composed of leaf litter and other organic matieral.

In what horizon is there very little organic material?

Horizon C had very little organic material.

What is the composition of horizon R?

Horizon R is composed of unweathered parent material.

How are horizon A and horizon C different?

Horizon A is rich in organic material and horizon C has very little organic

mateial.

Why do plants grow well in horizon A?

Plants grow well in horizon A because it is rich in organic material and

nutrients.