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4.7 Learning About Soil
Page 210-211
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Rocks can be broken down by weathering

These particles of rock are the beginning of a process that leads to the formation of soil in
which plants can grow

The soil can be views as a series of thin layers called horizons

Each layer can be identified by a distinct color, thickness, and texture

Mature soils in different biomes or geographic regions vary in color, porosity, acidity,
and depth

These characteristics can be used to classify different soil types
Litter
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The surface of the soil is usually covered with leaves, broken branches, and fallen
trees

This layer keeps the ground damp by preventing too much water from evaporating
Topsoil

Beneath the litter

Topsoil usually contains dark, decaying plant and animal matter called humus

Humus contains the rich supply of nutrients and minerals that new plants need for
growth
Subsoil

Contains larger pieces of rock and clay

Usually lighter in color as it contains little humus
Bedrock

A layer of solid, unbroken rock
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This layer is still subject to biological weathering
Bedrock to Topsoil

As bedrock is weathered, small rocks break off and become subsoil

The subsoil is also being weathered by plant roots, and small burrowing animals,
which brings humus down into the subsoil

As a result, the top of the subsoil, slowly becomes topsoil
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