By Jon Zamboni | Updated Aug 30, 2022

Pi-Lens/iStock/Getty Images

Weathering describes any natural process that disintegrates rocks at the Earth's surface. It encompasses both gradual wear and sudden fracturing, ultimately leading to erosion and large structural changes.

TL;DR (Too Long; Didn't Read)

Biological weathering is the breakdown of rock caused by living organisms—including plants, animals, fungi, and bacteria.

Biological Weathering vs. Physical and Chemical Weathering

ekina/iStock/Getty Images

Physical weathering results from mechanical forces that fracture rock without altering its chemical composition—for example, freeze–thaw cycles that split joints. Chemical weathering involves reactions between minerals and external substances, such as acid rain corroding rock surfaces. Biological weathering, on the other hand, is driven by organisms. While it can produce physical effects (e.g., tree roots prying apart rock) or chemical effects (e.g., root exudates forming acids), it often acts synergistically, weakening rock and exposing it to the other weathering modes.

Trees and Other Plants

itman__47/iStock/Getty Images

One of the most visible examples of biological weathering is a sidewalk cracked by a tree root. Roots penetrate gaps and fissures, applying pressure that widens fractures. They also contribute chemically: as roots die, the released carbon dioxide reacts with water to form carbonic acid, which slowly dissolves the surrounding rock into soil.

Microorganisms and Lichens

KirsanovV/iStock/Getty Images

Many microorganisms work beneath our feet or on rock surfaces, quietly breaking down minerals. Certain bacteria assimilate nitrogen from the air while extracting silica, phosphorus, and calcium from the rock; by removing these elements, the substrate becomes more susceptible to wind, water, and other forces. Lichens—symbiotic colonies of fungi and algae—also weather rock. The fungal partner secretes acids that dissolve minerals, and the algal partner draws nutrients from the resulting solution.

Animal Activity

cnmacdon/iStock/Getty Images

Animals can influence weathering in several ways. Foot traffic creates friction that wears away tiny particles over time. Burrowing mammals such as badgers and moles excavate rock, bringing it to the surface where it is exposed to further weathering. Some species, like the piddock clam, burrow directly into rock, carving cavities with their shells. Human activity—construction, mining, quarrying—also contributes to biological weathering by disrupting large rock volumes and creating new surfaces for erosion.