The processes of weathering which are mainly related to the activities of plants, animals and organisms like bacteria etc. are known as ‘Biological weathering. It involves the role of plants and animals in the breaking down of rocks through mechanical ways as well as in the decomposition of rocks.
Role of Plants and Animals in the Physical Breaking Down of Rock
(a) Plant-roots, growing between jointed blocks and along minute fractures between mineral grains, exert an expansive force tending to widen the existing openings and sometimes create new fractures.
(b) Insects like earth-worm, snail etc. and burrowing animals like rodents looser, the soil cover and create suitable conditions for the various external agencies to have their own action on the underlying rocks that lead to rock weathering.
Bio-chemical Process of Weathering
(a) The role of organisms in chemical weathering depends much on their ability to assimilate various elements from the rocks and to evolve various organic acids etc. Plant roots dissolve various constituents of the rocks with the acids evolved by the tips of their roots.
Besides, certain groups of bacteria algae and mosses breakup rock-forming silicates directly, removing from them elements like silica, potassium phosphorous, calcium, magnesium etc. that they need as nutrients. This facilitates rock-weathering.
(b) Bird droppings have been stated to be capable of weathering limestone’s.
(c) With the decay and degeneration of the dead remains of plants and animals, chemically active substances are produced like carbon dioxide, humic acid, together with traces of ammonia, nitric acid etc. These substances are capable of bringing about rock-weathering.
(d) Man himself is an important agent of destruction.
All the processes of weathering, physical, chemical and biological, are interconnected and act simultaneously.