Weathering: physical, chemical, and biological

Outer layers may peel due to temperature or pressure changes. Exam tip: onion-like layers indicate exfoliation.

The direct answer is A: removal or peeling of outer rock layers. Exfoliation is a type of physical weathering in which curved or sheet-like outer layers of a rock separate from the main mass. It may happen when pressure is released, when a rock repeatedly heats and cools, or when expansion and contraction create stress. Step by step: stress develops near the rock surface; cracks form roughly parallel to the surface; thin layers loosen and peel away; the exposed rock may become rounded. Option A is correct because it describes the defining feature of exfoliation. Option B is wrong because a long river valley is mainly a fluvial landform produced by river erosion, not the peeling of rock sheets. Option C is wrong because deposition of sea organisms may help form some limestone, but it is not exfoliation. Option D is wrong because cooling of magma forms igneous rock; it is not the later removal of outer layers by weathering. Exfoliation changes the shape of existing rock through physical forces and does not require chemical transformation. Memory cue: exfoliation is like a rock peeling in sheets, similar to layers coming off an onion.

Hard and resistant rocks oppose weathering more. Exam tip: connect rock properties with weathering rate.

Soft rocks have low resistance, so they weaken faster. Exam tip: low resistance means faster weathering.

Small pieces expose more surface, increasing reactions. Exam tip: remember the link between smaller particles and faster weathering.

Vegetation helps weathering through root pressure and organic substances. Exam tip: connect plants with biological weathering.

Microorganisms may produce chemicals that help alter minerals. Exam tip: microorganisms are also living agents.

Human activities can expose rocks and speed up weathering. Exam tip: understand humans as biological agents too.

Water supports both physical and chemical weathering. Exam tip: remember water as a very important factor.

Direct answer: A is correct. Weathering becomes faster when rock is directly exposed to the agents that act on it. Air supplies oxygen and carbon dioxide; water enters cracks and can cause chemical reactions; and repeated heating and cooling produces expansion and contraction. These effects can weaken minerals and enlarge cracks. On a slope, exposed rock may also have less protective soil or vegetation, so rain, wind and temperature changes reach it more directly. Option A correctly names air, water and temperature change. Option B is wrong because a rock does not need to detach from Earth in order to weather; detachment is more related to movement or mass wasting. Option C is wrong because rocks do contain minerals, and those minerals are what weather. Option D is wrong because exposed slope rocks are not always in the sea; marine conditions are not required. Memory cue: greater exposure gives weathering agents easier access, but the exact rate also depends on rock type, climate, joints and slope conditions.

Decaying organic matter can form acids that alter minerals. Exam tip: remember the link between humus and chemical change.

Some minerals react quickly while others are more resistant. Exam tip: connect mineral composition with weathering rate.

Cracks provide pathways for water and air. Exam tip: understand joints and cracks as entry routes for weathering.

Rock can break into debris and fine particles. Exam tip: remember debris and soil as products of weathering.

The direct answer is A, Weathering. Weathering means the breaking down or weakening of rock at the place where the rock is found. It does not require the broken material to be carried away. Step by step: first, rain, heat, cold, chemicals, plant roots, or animals act on exposed rock; next, the rock becomes cracked, weak, or chemically changed; finally, the material may remain there until erosion transports it. Option A is correct because weathering is an in-place process. Option B, river transportation, is wrong because a river carries sediment from one place to another; it is movement, not weakening at the original place. Option C, marine deposition, is wrong because deposition means sediments settle in a sea or coastal area. Option D, glacial accumulation, is wrong because accumulation means material is collected or deposited by a glacier. A useful memory cue is: weathering works where the rock is, while erosion transports what weathering produces.

Chemical reactions can create new minerals or new colours. Exam tip: treat colour change as a chemical sign.

The direct answer is A, chemical composition. Physical weathering breaks a rock into smaller pieces without normally changing the minerals into new chemical substances. The reasoning is: a large rock is cracked, split, expanded, contracted, or rubbed; the pieces become smaller; the total exposed surface may increase; however, the minerals generally remain chemically the same. Option A is correct because chemical composition is normally unchanged in physical weathering. Option B, size of pieces, is wrong because physical weathering commonly makes pieces smaller. Option C, number of particles, is wrong because one rock can break into many more pieces. Option D, surface area, is wrong because smaller fragments usually create a greater total surface area, although the exact increase depends on how the rock breaks. The word generally matters: physical weathering does not absolutely prevent every chemical change in nature, but its defining effect is mechanical breaking. Memory cue: physical weathering changes form and size, not usually the chemical identity.

Chemical weathering can change the nature of minerals. Exam tip: identify chemical weathering by change in composition.

The direct answer is A, entry and drying of salty water. Salt weathering occurs when salty water enters cracks or pores in rock and later evaporates. Step by step: salty water moves into a small opening; warm or dry conditions remove the water by evaporation; salt crystals are left behind and may grow; the growing crystals press against the walls of the opening; repeated wetting and drying can loosen grains and break the rock. Option A is correct because the wet-dry cycle supplies both salt and crystal growth. Option B is wrong because complete darkness without water provides no dissolved salt or wet-dry process. Option C is wrong because volcanic eruptions are not the normal cause of salt crystallisation in exposed rocks. Option D is wrong because plate collision may create mountains and pressure, but it is not the direct condition needed for salt weathering. Remember: salt weathering needs salt, water, evaporation, and repeated cycles.

Correct answer: A, biological weathering. Weathering means the breaking down or alteration of rock at or near its original place. When a plant root enters a small crack, it continues to grow and becomes thicker. Its pressure pushes against the sides of the crack, gradually widening it and helping the rock split. Because a living organism, the plant, causes this action, it is called biological weathering. A is correct because roots are living agents that physically break rock. B is wrong because marine deposition means the laying down of sediments by sea water, not the breaking of rock by roots. C is wrong because a seismic wave is energy from an earthquake, not a weathering category. D is wrong because magma flow involves molten rock inside or on the Earth, not root pressure. Memory cue: living organisms causing rock change means biological weathering.

In solution, soluble minerals mix with water. Exam tip: understand it as a chemical weathering process.

Weathering is a basic link in external processes changing the surface. Exam tip: connect it with landform development.

Weathering is linked with external agents on Earth surface. Exam tip: remember it as an exogenic process.

More cracks allow easy entry of water, air and roots. Exam tip: cracks are a factor increasing weathering.

In physical weathering, the chemical composition usually does not change. Link it with mechanical breaking in exams.