formation of soil and soil types

Formation of Soil and Soil Profiles

What is soil?• Soil is a mixture of weathered rock and

decayed plant and animal matter that formed over a long time.

• Soil is just as important as water, air, and sunlight.– Without soil, there would be no plants.– Without plants, there would be no food or

shelter for humans or animals.

What have you used today that depended on soil?

-Clothing (cotton grows in soil)

-Food (every plant and animal depends on soil, even wheat and flour for

bread)

-Shelter (wood comes from trees that grow in soil,

materials in drywall and concrete come from soil or depend on soil somewhere)

-School Supplies

Why does it take soil so long to form?

1. When rock is exposed at the surface, it begins to erode.

2. Mosses and other types of vegetation begin to grow.

3. Mosses and vegetation die and decay and become part of the soil.

4. Insects, worms, bacteria, and fungi start to live and grow and when they die they decay and form a material called “humus”.

5. Seeds of plants blow in and take root.6. As more organisms die, the soil

becomes more fertile. Animal droppings also add to the fertileness.

Soil Profiles

• Soil forms in layers.

• The set of layers is called a profile.

Soil Profiles

• Sometimes the layers are called horizons.

Soil Layers• The first layer or “O Horizon” is the

organic layer. – This is a layer of dead leaves and

organisms that are decaying into humus.

• The second layer or “A Horizon” is the topsoil layer. – This is where most plant roots are.

Soil Layers• The third layer or the

“B Horizon” is the subsoil layer. – This contains few

plant roots and many minerals that it gets from water seeping through the two top layers.

• The fourth layer or the “C Horizon” is the bedrock layer. – This is mostly rocks

and pebbles and this layer is just beginning the cycle.

Differences in Soils• The types of soil that form depend on

many factors. – Climate– Type of bedrock– Shape of the land– Amount of humus– Amount of time– Amount of water

• For example, the soil in the desert is different from the soil in a rainforest. Or clay is different from farming soil.

Review• What is soil?• Why is soil important?• How is soil formed?• What are the layers of soil?• What factors effect the type of soil?