Objectives:Explain how soil evolves from rock.Describe the differences in soil in the soil profile.Discuss how environmental conditions affect soil

Soil is weathered rock, organic matter, mineral fragments, water and air.

1.Rock is weathered

2. Plants grow

3. Worms, insects and bacteria add organic matter.

4. Humus develops from decaying plants and animals.

The soil profile is made of different layers or horizons of soil.

This is the layer of organic material.

Grass, trees, flowers, leaves and twigs (AKA: litter)

This is the top layer is also known as top soil. It is the most evolved for the rock from which it was created. Plant roots grow at this layer.

Called sub soil, this layer is less evolved from the first layer. It is lighter in color from the first layer. It also contains less minerals.

This horizon contains partly weathered rock that is beginning the long process of becoming soil.

Soil profiles look different from place to place.Soil horizons are thinner where there is little rainfall.

Soil development is effected by several factors.•Climate – The more rain, the faster soil develops (rainforest)•Time•Slope of the land effects the distribution of soil layers.

The United States has nine soil groups.