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Soil is formed through the process of rock weathering. Weathering is the breakdown of rocks into smaller particles when in contact with water (flowing through rocks), air or living organisms. Weathering can occur physically, biologically or chemically.

Physical weathering: This is the disintegration of rocks into smaller particles with no alteration in their molecular structure. Air and water are agents of physical weathering. Windblown on rocks, heavy downpour of rain, water waves from the sea can facilitate a gradual fragmentation of rock particles to sediments which eventually become soil.

Chemical weathering: In chemical weathering chemical reactions within rocks create changes in their mineral composition. Examples of chemical reactions leading to weathering are hydrolysis, carbonation, oxidation and hydration.

• Hydrolysis: hydrolysis occurs as rain water seeps through rocks and the hydrogen ion (H+) in water reacts with metallic ions in rocks resulting in dissolution of rock minerals.

• Carbonation: During carbonation carbon dioxide from the air and from living organisms dissolve in water to form carbonic acid. This acidifies water in rocks leading to further chemical reaction with rock minerals.

• Oxidation: in oxidation oxygen from the air reacts with iron in rocks to form iron oxides. This reaction creates a rusty brown colouration on rocks.

Biological weathering: In this process biological organisms facilitate rock fragmentation. Tree roots and mosses grow or penetrate through rocks and create pore spaces which gradually pull rocks apart. Animals burrow through rocks and create disintegration. Micro organisms like lichen (a symbiotic relationship between fungi and algae) release chemicals which break down rock minerals.

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