Define weathering and differentiate between mechanical weathering and chemical weathering, with examples.

• A. Weathering is only chemical; mechanical weathering doesn't exist.
• B. Mechanical weathering occurs only in deserts.
• C. Weathering is breakdown of rocks at/near the surface; mechanical: physical breakup (freeze-thaw, exfoliation); chemical: chemical alteration (oxidation, hydrolysis, carbonation).
• D. Chemical weathering requires high temperatures only.

Answer: (C)

Weathering is the breakdown and alteration of rocks at or near the Earth’s surface. It happens in two broad forms: mechanical weathering, which physically splits rocks into smaller pieces without changing their mineral identity, and chemical weathering, which changes the minerals themselves or dissolves them.

Mechanical weathering involves processes that don’t change what the rock is made of, just its size and shape. Freeze-thaw (or frost wedging) is a classic example: water works into cracks, freezes, expands, and pushes the crack wider, gradually breaking the rock apart. Exfoliation happens when overlying pressure is released as rock is eroded away, causing outer layers to peel off. Abrasion wears surfaces down as wind, water, or ice carrying particles grind against the rock.

Chemical weathering changes the rock’s chemical composition. Oxidation alters minerals containing iron, giving rusty colors as they form iron oxides. Hydrolysis reshapes minerals like feldspars into clay minerals and dissolved ions. Carbonation dissolves calcite in limestone when carbon dioxide-rich water forms a weak acid, producing dissolved calcium ions and bicarbonate.

Both processes contribute to soil formation and the creation of regolith, and they often occur together, with mechanical weathering increasing surface area and thus accelerating chemical weathering. The described combination—weathering as surface breakdown, with mechanical weathering as physical breakup and chemical weathering as chemical alteration—matches how weathering actually operates.