Soil A mixture of weatheredrock, organic matter, mineralfragments, water, & air.

Humus Dark-colored organic matterfound in soil; made ofdecayed plants & animals.

SoilProfile

A vertical view of soil layers(horizons).

Horizon A soil layer. Most areas ofthe Earth have 3 basichorizons (A, B, & C).

Leaching Process that occurs whensoil materials dissolved inwater are carried downthrough the soil layers.

OLayer

This layer has a lot ofdecaying leaves & twigs.Very rich in humus. Verydark in color. Very fewrocks. Part of our topsoil.

ALayer

Also part of our topsoil.Material from the O layerleaches down into this layer.Also very dark in color.Mostly humus & weatheredclay. Very few rocks.

BLayer

VERY LITTLE humus.Lighter in color. More clayand small rocks than upperlayers.

CLayer

Almost no humus. Mostlyclay, sand, and larger broken-off pieces of bedrock.

Bedrock The solid layer of rockbeneath the 3 major soillayers.

DecomposersOrganisms that break downthe remains of dead plantsand animals.

Litter The loose layer of leaves orplant remains on the ground.

Erosion The process by which wind,ice, water, or gravity movesweathered rock or soil.

Nutrients Chemical substances in soilthat plants and animals needin order to live.