Weathering, which refers to the gradual erosion and transformation of rocks on Earth, occurs over time with exposure. Some rocks change faster than others depending on how exposed they have been for an extended period of time.
Chemical Weathering occurs when minerals that were once stable inside a rock convert into less stable forms at Earth’s surface, potentially leading to its disintegration. This process often leads to rocks crumbling away.
Physical
Physical weathering refers to the gradual weakening and disintegration of rocks due to physical forces such as temperature fluctuation, abrasion and frost action (freezing and thawing). Physical weathering breaks large blocks of rock into smaller pieces without changing their chemical composition; by breaking apart these larger blocks further surface area is exposed, speeding up chemical weathering processes faster.
Granulated sugar dissolves more rapidly in water due to its larger surface area; similarly, physical weathering enhances chemical weathering by making mineral particles within rocks more accessible to elements that can break them down.
Weathering can also be caused by thermal stress. This occurs when rocks heat up under sunlight and then cool off again as temperatures fluctuate, expanding and contracting as pressure builds on their outer layers, eventually wearing away through exfoliation. Burning fossil fuels speeds up physical weathering by adding sulfur dioxide and other chemicals that form acid raindrops – quickly weathering limestone, marble and other types of rock.
Chemical
Chemical weathering processes break down rocks and minerals by altering their composition – this includes oxidation, hydrolysis and carbonation processes.
Water can weaken rocks such as granite by dissolving feldspar crystals and creating clay minerals, weakening and eventually disintegrating its structure. This makes breaking away more manageable.
Chemical weathering involves rocks containing iron that rust when exposed to oxygen and water; this oxidation process further erodes away at rock structures, increasing rates of erosion.
Chemical weathering releases minerals into the earth that form soils, consisting of tiny fragments from various types of rock and materials that come together with organic matter (decomposed plants and animal remains) to form fertile environments for plant life to flourish in.
Biological
Biological weathering occurs when plants, animals and microorganisms work to break down rock. Lichens–fungi and algae living together in an intimate symbiosis–eat away at rock surfaces while also creating physical weathering by widening cracks and creating pores in rocks. Burrowing animals such as shrews and moles as well as pecking birds can accelerate physical weathering by applying additional pressure onto rocks causing greater physical weathering effects.
Roots from plants can also contribute to physical weathering by growing into gaps and spaces in rocks, while lichens help chemically weather rocks by secreting acids that alter how minerals break down in rocks, leading to further weathering and making it brittle and susceptible to further weathering. Furthermore, microbial activity alters rock’s chemical composition, making it even more prone to physical and chemical weathering processes.
Human
Human activities over time have had a profound effect on rates and patterns of weathering. Digging and blasting rock for homes, roads, subways etc causes mechanical weathering that exposes more surfaces for chemical weathering; chemical weathering is further increased when burning fossil fuels produces nitrogen oxide and sulfur dioxide into the atmosphere; when combined with raindrops from falling raindrops this creates acid rain which rapidly weathers limestone and marble surfaces, making gravestone inscriptions harder to read as well as harming historic buildings.
Social injustice can have far-reaching repercussions for our physical and mental wellbeing, including epigenetics (which measures how genes respond to our environment) and allostatic load (the wear and tear on body systems from chronic stress). Weathering’s effects can be seen in communities experiencing poverty, long commutes, eviction threats or broken support networks – conditions which lead directly to weathering effects.