Biological Weathering of Rocks
Unlike physical and chemical weathering, the biological or living agents are responsible for both decomposition and disintegration of rocks and minerals. The biological life is mainly controlled largely by the prevailing environment.
1. Man and Animals:
The action of man in disintegration of rocks is well known as he cuts rocks to build dams, channels and construct roads and buildings. All these activities result in increasing the surface area of the rocks for attack of chemical agents and accelerate the process of rock decomposition.
A large number of animals, birds, insects and worms, by their activities they make holes in them and thus aids for weathering.
In tropical and sub tropical regions, ants and termites build galleries and passages and carry materials from lower to upper surface and excrete acids. The oxygen and water with many dissolved substances, reach every part of the rock through the cracks, holes and galleries, and thus brings about speedy disintegration.
Rabbits, by burrowing in to the ground, destroy soft rocks. Moles, ants and bodies of the dead animals, provides substances which react with minerals and aid in decaying process
The earthworms pass the soil through the alimentary canal and thus bring about physical and chemical changes in soil material.
2. Higher Plants and Roots: The roots of trees and other plants penetrates into the joints and crevices of the rocks. As they grew, they exert a great disruptive force and the hard rock may break apart. (e.g.) pipal tree growing on walls/ rocks
The grass root form a sponge like mass prevents erosion and conserve moisture and thus allowing moisture and air to enter in to the rock for further action.
Some roots penetrate deep into the soil and may open some sort of drainage channel. The roots running in crevices in lime stone and marble produces acids. These acids have a solvent action on carbonates.
The dead roots and plant residues decompose and produce carbon dioxide which is of great importance in weathering.
3. Micro- organisms: In early stages of mineral decomposition and soil formation, the lower forms of plants and animals like, mosses, bacteria and fungi and actinomycetes play an important role. They extract nutrients from the rock and N from air and live with a small quantity of water. In due course of time, the soil develops under the cluster of these micro-organisms.
This organism closely associated with the decay of plant and animal remains and thus liberates nutrients for the use of next generation plants and also produces CO2 and organic compounds which aid in mineral decomposition.