Weathering wears away at rocks’ surfaces over time. Exposure time determines how much alteration, dissolution and physical breakup will occur as a result.
Chemical weathering alters the molecular structures of minerals found in rocks. Silicate minerals may, for instance, decay by dissolving into clays or becoming dispersed through waterways.
Mechanical
Mechanical weathering involves breaking rocks apart without changing their chemical makeup, typically through water as a major agent. Water seeps into cracks and crevices in rock, freezes over when temperatures dip, expanding as it does so and breaking apart pieces. Rain or stream flow may also help cause mechanical weathering through an action called abrasion; and wind-blown grit may even contribute to mechanical weathering as it rubs against surface rocks making them smoother and smaller over time.
Smaller rocks tend to wear down faster due to having more surface area. Animals such as ants and worms that burrow, such as ants and worms, also contribute by shifting sand around and exposing fresh surfaces for weathering processes to attack. Also, daily temperature cycles can weaken rocks enough for them to break apart, all processes which are examples of erosion as discussed previously in this chapter.
Chemical
Chemical weathering involves altering rocks’ structures by altering their chemical composition, rendering them easier to break apart in wetter climates than physical weathering. It happens much quicker in this instance.
Chemical weathering processes such as oxidation (rusting), hydrolysis (breakdown by acidic water), and carbonation (reactions with rainwater that contains dissolved carbon dioxide) are examples of weathering phenomena. Since chemical reactions tend to take place at higher temperatures, they’re more likely to happen in warmer regions.
Different minerals weather at different rates. Quartz crystals tend to be more stable than their feldspar and olivine counterparts due to them forming at lower pressures and temperatures than quartz.
Minerals react differently with weather, depending on their degree of reactivity. More resistant minerals tend to breakdown first than more sensitive ones, leading to richer soil than its mixture counterparts.
Biological
Biological weathering occurs when plant roots or other living organisms break rocks into smaller pieces through chemical action such as water, ice, acids and salts; but also by microorganisms and temperature variations. Humans may contribute to this form of weathering by unwittingly kicking rocks or mining for minerals containing precious ores.
As long as there are microorganisms present, their presence can accelerate weathering processes of rocks or minerals. Carbonic acid from rainwater or seawater seeping through limestone causes carbonation of its rock structure (carbonation). Chemical weathering can also be hastened through organic acids taken up by plants with mycorrhizal fungi as part of their mycorrhizal relationships.
Recent studies utilizing techniques such as atomic force microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and vertical scanning interferometry have demonstrated mycorrhizal fungi altering mineral structures across a spectrum of minerals. Their presence boosted mineral dissolution rates; hence their inclusion should be taken into consideration when designing future models.
Human
Humans weather in various ways. One such way is the combustion of fossil fuels which increases air pollution by emitting nitrogen oxide and sulfur dioxide gasses into the atmosphere, where they react with sunlight and moisture to form acids which fall back down as acid rain – quickly weathering limestone, marble, gravestones, and even making gravestone names unreadable.
Plants, fungi, and other living things can also contribute to weathering processes. For instance, plant roots may find their way between cracks in rocks to slowly widen them before eventually breaking apart and being carried away by water currents, winds or glaciers for erosion purposes.
Geronimus’ weathering hypothesis is rapidly gaining support in the scientific community, most notably after she recently explained it on National Public Radio (NPR). According to Geronimus, chronic stress from socioeconomic hardship, political marginalization, racism, and persistent discrimination can wreak havoc on a person’s heart, arteries, brain, neuroendocrine systems resulting in multiple health complications that eventually contribute to early deaths.