How Does Biological Weathering Happen?
Weathering is the process through which rocks, soils, minerals, and other materials are broken down through contact with physical or atmospheric forces, such as pressure and heat, or chemical forces, such as acids. Similar to erosion, weathering can result in caverns, caves, burrows, and other unique rock formations. Biological weathering is a form of both physical and chemical weathering wherein living organisms directly and indirectly cause the decomposition the rock and other materials. Weathering is critical in the movement of nutrients and groundwater, as we'll see a bit later. Common inducers of biological weathering include animals, plants, and strange organisms called lichens.
How Animals Affect Weathering:
A lot of animals physically weather rocks and rock particles. Gophers for example, break apart the earth when they bore underground, separating rock compounds to dig tunnels. Other animals like worms and termites also decompose rocks and minerals in the same fashion. Animal death serves as an indirect form of biological weathering. When animals die, they decay, releasing carbon dioxide into the atmosphere. This carbon dioxide can then combine with water to form carbonic acid, a chemical capable of decomposing minerals.
Plant roots are arguably the most significant cause of biological weathering due to their widespread impact on the earth’s soil.
How Plants Affect Weathering:
Plants weather the earth in a similar way to animals, their roots often being to blame. Plant roots bore into the earth in the same way gophers and worms do, physically shattering rocks and creating cracks throughout the ground. In addition, many plants release acidic and chelating compounds (like organic acids) in order to break down metal-containing particles in the soil. Plants also produce organic acids when they decay, causing further decomposition.
How Lichens Affect Weathering:
Lichens are composite organisms. This means that lichens consist of two individual organisms that coexist with each other in a symbiotic relationship. Lichens usually consist of fungi and either algae or cyanobacteria (a bacteria that undergoes photosynthesis like plants). Lichens contains microscopic filaments that find their way into small cracks between rocks, repeatedly engorging and shrinking to increase the size of the gaps. This allows more lichens to enter and continue creating fissures in the rock. Lichens also produce oxalic acid, which siphons calcium carbonate from within the rock to its surface and replacing it with a weaker compound, thereby making it easier for the rock to erode. The calcium carbonate is then easily washed away by rain.
Biological weathering sounds an awful lot like erosion, but there is a key difference between the two. Erosion is when the earth’s surface is worn away by moving factors, like running water or wind. Weathering, on the other hand, is a stationary process.
Why Does It Matter?
Biological weathering, and weathering in general, is a crucial process to life on Earth. When rocks are broken down physically or chemically, nutrient rich minerals are released, nourishing plants. Often the types of plants growing in a certain area depend on how the rock and soil have been weathered. The water cycle is also heavily influenced by biological weathering. Agents of biological weathering, plant roots especially, create crevices and tunnels that act as paths used in natural water filtration, cleaning the groundwater that many organisms depend on. As seen with the gopher burrows, biological weathering is an excellent way to create suitable habitats for many creatures; burrows for gophers, caverns for bats, small crevices for plants and lichens - weathering provides all of these diverse homes for the equally diverse organisms that dwell within them.
A Quick Example:
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