Biological Activity and Weathering

Biological weathering is not a separate, exotic process — it is simply the contribution that living organisms make to the ordinary chemical and physical weathering already underway. The definition to hold onto is this: biological weathering is the contribution to, or removal of, minerals and ions from the weathering environment, plus the physical changes caused by the growth or movement of organisms. In other words, life speeds up, redirects, and sometimes directly causes the breakdown of earth materials.

The most obvious physical route is burrowing and wedging. Organisms like earthworms, termites, and rodents dig through soil and rock debris, and in doing so they do two things at once. First, they expose fresh surfaces that were previously buried and protected, handing those new surfaces over to chemical attack. Second, their tunnels and burrows let moisture and air penetrate deeper into the ground than they otherwise would. Both effects multiply the rate of weathering far beyond what the organism's own strength could achieve.

Human beings belong in this list too, though our role is less deliberate. By disturbing vegetation, ploughing fields, and cultivating soil, we mix earth materials and create new contacts between air, water, and minerals. Every time a field is turned over, fresh mineral surfaces meet oxygen and moisture, and weathering gets a fresh start. We are, in effect, biological weathering agents whether we intend it or not.

The chemical side of biological activity comes largely from decay. When plant and animal matter decompose, they produce humic acid, carbonic acid, and other organic acids. These acids seep into the weathering environment and do real chemical work: they enhance the decay of minerals and increase the solubility of certain elements, making those elements easier to dissolve and remove. Dead matter, then, is not just passive debris — it is a chemical factory feeding the weathering process.

Finally, plant roots exert tremendous pressure on earth materials. As roots grow and thicken, they mechanically pry apart rocks and soil, literally breaking them apart from within. This is wedging in the same family as the burrowing of earthworms, but on a larger and often more forceful scale. …