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Question
Natural factors, such as wind, rain, etc., help in the formation of soil from rocks. Is this change physical or chemical and why?
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Concept:
5.7.1 Weathering of Rocks
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Answer
Soil formation from rocks — called
weathering
— involves
both physical and chemical
changes.
Physical changes during weathering:
- Wind and rain wear down rock surfaces.
- Temperature changes (hot days, cold nights) cause rocks to expand and contract, cracking them.
- Water freezing in cracks expands and splits rocks open.
- Tree roots growing into cracks widen them.
- All these only break the rock into smaller pieces — no new substance is formed.
Chemical changes during weathering:
- Water and chemicals in water react with minerals in the rock.
- For example, iron in basalt rock reacts with water and air over time to form iron oxide (red layer).
- This forms new substances , so it is a chemical change.
Soil formation is therefore a combination of physical and chemical processes — we collectively call it weathering .
