Weathering

Weathering is the breakdown and chemical alteration of rocks at or near the Earth's surface by physical, chemical, and biological processes. It operates in place, in contrast to erosion, which removes weathered material and transports it by wind, water, or ice.

Weathering occurs through three interrelated pathways. Physical or mechanical weathering disintegrates rocks without changing their mineral composition. Key processes include frost wedging from freeze–thaw cycles, exfoliation from pressure release, thermal expansion and contraction, abrasion by windblown particles, and salt crystallization that exerts pressure in pores.

Chemical weathering involves chemical reactions that dissolve or alter minerals, typically in the presence of water and atmospheric gases. Common processes include hydrolysis of feldspars to form clays, dissolution of calcite by carbonic acid, oxidation of iron-bearing minerals to form ferric oxides, and carbonation where carbon dioxide in water dissolves minerals.

Biological weathering encompasses the actions of living organisms. Plant roots can pry rocks apart and secrete organic acids; lichens and mosses produce acids that chemically attack surfaces; microbes can accelerate both physical and chemical weathering.

Rates of weathering depend on climate, rock mineralogy, and the degree of physical weathering already present. Warm, wet climates generally promote chemical weathering and faster rates, while cold or arid conditions slow chemical processes and favor physical fragmentation. Weathering contributes to soil formation and regolith development, releases nutrients and ions into ecosystems, and shapes landscapes over geological timescales.