Biological weathering is the effect that living organisms, such as plants and animals, have on rocks and other inanimate objects. This phenomena happens due to the molecular breakdown of minerals in the rock. When biological weathering occurs, the living organism breaks down the rock or other nonliving object through either mechanical or chemical erosion or the use of both.
An example of mechanical biological weathering is tree roots growing through a rock, slowly prying it apart or breaking the rock into pieces. Once the tree roots create the holes for the roots to go through, the roots can leech the nutrients from the rock. Another example is an animal that secretes an acid or bores its way into a rock by slowly eroding the space and sliding into it. Either of these methods works to dissolve the rock over time. Organisms such as bacteria, algae and lichen secrete chemicals that work to break down the rocks on which they live. This provides for the slow dissolution of the rock while the organism is still pulling the nutrients it needs to survive from the rock. Organisms such as moss, lichen and algae primarily are found near water sources where the climate is humid, damp and shaded. In this type of climate the organism can grow unimpeded.