Page 1 - 2. Lesson notes- Mineral riches in the soil

SAI International School
Subject- Biology
Chapter- Natural Resources
Subtopic- Mineral riches in the soil
Module- 33
Lesson Notes

Mineral Riches in the Soil.

• The soil is the top surface layer of the earth's crust.

• It is formed by the breakdown of rocks over a long period of time by various physical,
chemical and biological processes.

• The fine particles thus obtained is called soil.

Composition of soil

Soil is mainly composed of air, water, humus, microorganisms and minerals. These enhance
the quality and fertility of the soil and thereby, provide nourishment to the plants.

Process or formation of soil
i. Physical Processes

▪ Sun

The rocks expand by the heat of the sun. These rocks cool down and contract at night. This

expansion and contraction of rocks result in the formation of cracks in the rocks. As a result,
the huge rocks break into smaller pieces.

▪ Water

The water enters into the cracks formed due to the heating by the sun. This water when freezes

widen the cracks. When rocks are in contact with flowing water for a longer period of time, it
results in wearing of the rocks. Also, the rock particles present in the flowing water rub against

the rocks and break it into smaller particles. These particles are carried by water and deposited

as soil on its way.

▪ Wind

Strong winds erode the rocks and carry the sand from one place to another.