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HOW DOES SOIL FORM?
Transcript of HOW DOES SOIL FORM?
1. Summarize how soils form.
2. Explain how the composition of parent rock affects soil composition.
3. Describe the characteristic layers of mature residual soils.
4. Predict the type of soil that will form in arctic and tropical climates.
a loose mixture of rock fragments and organic material that can support the growth of vegetation
One result of weathering is the formation of regolith, a layer of weathered rock fragments that covers much of Earth’s surface.
Bedrock is the solid, unweathered rock that lies beneath the regolith.
The characteristics of soil depend mainly on the rock from which the soil was weathered, which is called the soil’s parent rock.
Soil composition refers to the materials of which it is made.
The color of soil is related to the composition of the soil.
Soil moisture can also affect color. SOIL TEXTURE:
Rock material in soil consists of three main types: clay, silt, and sand.
Clay particles have a diameter of less than 0.002 mm. Silt particles have a diameter from 0.002 to 0.05 mm. Sand particles have diameters from 0.05 to 2 mm.
The proportion of clay, silt, and sand in soil depends on the soil’s parent rock.
a vertical section of soil that shows the layers of horizons horizon:
a horizontal layer of soil that can be distinguished from the layers above and below it; also a boundary between two rock layers that have different physical properties
dark, organic material formed in soil from the decayed remains of plants and animals
The A horizon, or topsoil, is a mixture of organic materials and small rock particles.
The B horizon or subsoil, contains the minerals leached from the topsoil, clay, and sometimes, humus.
The C horizon consists of partially-weathered bedrock.
Climate is one of the most important factors that influences soil formation.
Climate determines the weathering processes that occur in a region.
In humid tropical climates, where much rain falls and where temperatures are high, chemical weathering causes thick soils to develop rapidly.
Leached minerals from the A horizon sometimes collect in the B horizon.
Heavy rains, which are common in tropical climates, cause a lot of leaching of the topsoil, and thus keep the A horizon thin.
A thin layer of humus usually covers the B horizon.
In temperate climates, where temperatures range between cool and warm and here rainfall is not excessive, both mechanical and chemical weathering occur.
All three soil horizons in temperate soils may reach a thickness of several meters.
Desert and Arctic Soils
In desert and arctic climates, rainfall is minimal and chemical weathering occurs slowly.
As a result, the soil is thin and consists mostly of regolith-evidence that soil in these areas form mainly by mechanical weathering.
Desert and arctic climates are also often too warm or too cold to sustain life, so their soils have little humus.