Organic weathering
FOCUS QUESTIONS:
1. What is biological/organic weathering? 2. What are the primary agents of biological weathering? 3. What are the examples of biological weathering and the processes involved? 4. What is the difference between physical weathering, biological and chemical weathering?
REMINDER OF WHAT WEATHERING IS:
Weathering is the break-up and decomposition of rocks in situ (in their place of origin).
BIOLOGICAL WEATHERING:
is the weakening and subsequent disintegration of rock by plants, animals and microbes
is a type of weathering brought about by various activities of living organisms takes place when rocks are worn away by living organisms causes molecular breakdown of minerals Biological weathering is of two types: by physical means by chemicals and organic compounds The primary agents in biological weathering are: Plants Animals
PLEASE NOTE:
These agents release acid-forming chemicals that cause weathering and contribute to the breaking down of rocks and landforms.
Biochemical processes, root penetration and animal burrowing are some of the processes determining biological weathering.
Organic compounds emit acidifying molecules that corrode rock minerals and, as such, make them weak and prone to disintegration.
Organisms such as moss, lichen and algae, primarily, are found near water sources where the climate is humid, damp and shaded.
TYPES OF BIOLOGICAL WEATHERING:
Growing plant roots can exert stress or pressure on rock. Although the process is physical, the pressure is exerted by a biological process (i.e., growing roots). Some plants and trees grow within the fractures in the rock formation. As they penetrate the soil, and their roots get bigger, they exert pressure on rocks and make the cracks wider, and deeper, which weaken and eventually disintegrate the rocks.
There are many small animals that bore holes in the rock and live inside it. Over time, they burrow and widen cracks and end up breaking rocks apart. Burrowing animals such as moles, squirrels, and rabbits can speed up the development of fissures. As this process continues, gaps and holes develop within the rock, further exposing the rocks to chemical, biological and physical weathering.
Lichens (organisms comprising fungi and algae), bacteria and mosses live on and feed on rocks, constantly altering the structure of the rock. Some plant microbial activity releases organic acidic compounds. These compounds can break down iron and aluminium minerals in the rocks, the outer layer of the rock, by altering the rock’s chemical composition.
Human activities equally dig, crash and widen the cracks and wind up fragmenting the rocks apart. These activities include mining, road construction and housing developments.
SUMMARY FOR ALL THREE TYPES OF WEATHERING:
The three types of weathering (biological, physical and chemical) work together to change and alter the structure of rocks. They can be independent of one another or two of these weathering behaviours can occur together. Scientists rely on weathering and erosion to reveal fossils in rock wall. This enables them to study rocks and changes in the Earth’s structure from thousands of years ago to the present.