Solid rock exposed at the surface slowly disintegrates and decomposes. Weathering is the in-place breakdown of rocks and minerals by physical, chemical, and biological processes. It differs from erosion in that the material is not removed, only prepared for later transport.

Physical weathering includes frost wedging, thermal expansion, and abrasion. Chemical weathering involves dissolution, oxidation, hydrolysis, and other reactions that alter mineral composition. Organisms contribute through root growth, organic acids, and microbial activity. Climate strongly influences which processes dominate.

Weathering produces regolith and soil, releases mineral nutrients, and contributes dissolved ions to rivers and the oceans. It is the essential first step in the sedimentary rock cycle. Rates of weathering affect landscape evolution and the long-term carbon cycle through the consumption of CO₂ by silicate mineral reactions.

• In-place breakdown of rock at the surface
• Physical, chemical, and biological processes
• Produces soil and prepares sediment
• Rate controlled largely by climate