Weathering refers to the decomposition of rock due to physical, chemical or biological forces.
Rocks that contain iron are susceptible to chemical weathering through oxidation – the process by which minerals turn into rust – making the rock weak and easier to break apart.
Physical
Physical weathering refers to any process which breaks rocks down without altering their chemical makeup, including forces such as water, ice, winds or gravity. Changes in temperature may also cause rocks to expand and contract over time causing physical weathering to take place; for instance in desert environments freeze-thaw cycles occur as water seeps into cracks then freezes then thaws repeatedly increasing pressure within them and eventually cracking apart rocks.
“Exfoliation” is another type of physical weathering. This occurs when a layer of rock is stripped away and pressure on it declines, allowing fractured pieces of rock to lie parallel with the land surface and fracture into sheets that lie parallel. Plants and animals can also physically weather rocks; for instance tree roots can enter tiny cracks in rocks before widening those same cracks over time; this process is known as root wedging.
Chemical
Chemical weathering involves rocks becoming weaker through changes to their minerals. Water often plays a part in this process as its elements interact with minerals present within rocks to form new minerals; for instance feldspar crystals in granite may become clay minerals when exposed to moisture, weakening and making the rock easier to break apart – this phenomenon being more likely in humid climates.
Acidic rainwater contributes to chemical weathering as well. Carbon dioxide from the atmosphere interacts with oxygen in rainwater to form carbonic acid, a weak acid capable of dissolving limestone found along coastal areas as well as creating huge cracks in rocks that make up caves like Carlsbad Caverns in New Mexico.
Biological weathering refers to the actions of plants and animals which wear away or break rocks over time. Rabbit burrowing into cracks in rocks can widen them, which ultimately causes their fragmentation; plant roots growing through rock openings can also contribute to this process.
Biological
Biological Weathering (BW) refers to the physical degrading of rocks and subsurface materials by living organisms. Plant roots tend to penetrate cracks or holes in rocks and exert pressure which further weakens them while lichen-producing fungi break down rocks chemically by altering their composition.
BW contributes to the formation of sedimentary rocks such as sandstones and limestones, and aids soil formation by contributing particles of clay, silt, and sand. Furthermore, minerals derived from broken down rocks provide essential nutrition to plants and animals alike.
Quantifying the contribution of living organisms to weathering can be challenging due to no pure abiotic controls existing and field-laboratory studies yielding variable results. Yet it seems likely that organisms contribute significantly to mineral weathering by breaking through bottlenecks in its overall process; for instance, fungi have been known to enhance mineral weathering by targeting specific minerals with nutritional value for soil enrichment.
Human
Human weathering, however, results from psychological stress and the consequent efforts to cope with it. Studies have linked psychological stress with an array of health indicators like cortisol levels, sympathetic nerve activity, blood pressure reactivity, cytokine production, waist-to-hip ratio and glycated hemoglobin.
Human weathering is hastened by air pollution, which converts atmospheric chemicals to acids that fall back down as acid rain. But many social measures which accelerate weathering — like living in low-income neighborhoods or experiencing discrimination or trauma–also lower quality of life and increase risks such as heart disease, stroke, diabetes and other health conditions.
Weathering’s effects are both far-reaching and complex; therefore addressing it requires taking an integrated approach that encompasses policies designed to promote socioeconomic stability, education, and healthcare access – as well as finding healthy ways for individuals to cope with systemic racism such as consulting a mental health professional for sessions.