The Process of Origin of Soil

Soil is a naturally occurring unconsolidated particulate material. The process of formation of soil is called pedogenesis. Soils are formed by two processes.

1. Weathering of rocks (Inorganic Soil Examples: Gravel, Sand, Silt, Clay, etc)
2. Decomposition of organic matter (Organic or Cumulose soils; Examples: Peat, Humus, muck, etc)

Types of weathering

Weathering of rock can occur in two ways.

1. Physical weathering
2. Chemical weathering

Physical weathering

It occurs due to physical effects like temperature, abrasion, splitting action of ice, penetration of plant roots, etc. Physical weathering results in no change in the chemical composition of particles. Physical weathering produces the following two types of soils.

1. Gravel
2. Sand

Chemical weathering

It is due to chemical actions like oxidation, hydration, carbonation, solution, leaching, hydrolysis, etc. Original rock minerals are transformed into clay minerals.  Physical weathering produces the following two types of soils.

1. Silt
2. Clay

Geological cycle

Weathering of rock followed by transportation of soil which is then deposited at one place to form the rock (upheaval) again. This is called the geological cycle.