Page 226 - New Medley 5 Semester 2

Soil forms from rocks, branches and dead animals

by wind and water. ese particles are further acted upon by other factors like

temperature changes, frost and living organisms. Natural events like earthquakes
also cause the huge rocks to break down into small pieces. It takes about 200 to

400 years for the formation of just 1 centimetre of topsoil.

Composition of Soil
ere are three layers of soil. ese are topsoil, subsoil and bedrock.

 Topsoil is the uppermost dark

layer of soil. It is the most fertile
layer because it is rich in humus. Humus

Humus is formed by the break Topsoil
down of dead and decaying parts

of plants and animals.
Subsoil
 Subsoil is found just below the
topsoil. It is a light-coloured

layer which contains little humus. Weathered
Below the subsoil, there is a layer parent rock

of lumps of parent rock.

 Bedrock is the lowest layer Bedrock or
of the soil. It is non-porous, parent rock

unweathered rock. Layers of soil

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