Page 84 - Science Class 07

9 9 9

Soil — Formation, Composition

and Importance

• Components of Soil • Forma on of Soil • Soil Profiles
• Textures of Soil • Types of Soil in India
• Moisture in Soil • Soil Erosion

Soil is a complex mixture of minerals, water, air,
organic ma er and countless organisms that
are the decaying remains of once-living things.
It forms at the surface of land and it is the “skin Top Soil
of the earth.”

Soil is capable of suppor ng plant life and is Sub Soil
vital to life on the earth.
Bed Rock
COMPONENTS OF SOIL
Layers of Soil
The soil broadly consists of the following
v Organisms : Soil also contains small living
components:
organisms such as bacteria, fungi, algae,
v Inorganic materials : Soil contains protozoans, earthworms, snails, ants, etc.
inorganic materials, i.e., mineral par cles. These organisms help in increasing the
These are derived from some parent fer lity of the soil and making it porous.
material, the soil forming rocks by
FORMATION OF SOIL
fragmenta on or weathering.
Soil is formed by the process of ‘weathering’ of
v Organic materials : Soil also contains
rocks, that is, disintegra on and decomposi on
organic materials in the form of humus. It
of rocks and mineral at or near the earth’s
is derived from dead organisms by the surface through the ac ons of natural or
process of decomposi on. mechanical and chemical agents into smaller

v Air and water : The gaps between the soil grains.
par cles contain air and water. Air and Factors affec ng forma on of soil may be
water are important cons tuents of soil. atmospheric, such as changes in temperature

84 Science-7