Weathering refers to the gradual destruction or degradation of rocks and minerals at Earth’s surface by weather conditions; this contrasts with erosion which involves movement by water, ice or wind.
Chemical weathering alters rock composition by reacting with water molecules; for instance, anhydrite reacts with it to become gypsum.
Physical
Physical weathering occurs when rocks are broken down by means of abrasion (contact with other objects such as wind, sand or water) and frost action (freezing and thawing) over time, ultimately resulting in exfoliation.
Physical weathering is caused by spontaneous fluctuations in temperature that cause rocks to expand and contract at different rates, leading to surface rupture through what’s known as abrasion – one reason igneous rocks such as granite and basalt crumble so readily.
Frost wedging is a form of physical weathering involving freezing and thawing cycles. Frost wedging occurs when water seeps into cracks in rock, then temperature drops and it freezes, acting like an ice wedge to slowly widening existing cracks while cracking apart rock over time.
Physical weathering breaks apart rocks to expose more surface area for chemical weathering to take effect; this allows more of the rock’s surface area to be exposed for chemical weathering, speeding up its progress like melting sugar lumps into granulated sugar over time.
Chemical
Chemical weathering occurs when water interacts with minerals in rocks to alter their composition and alter how they behave, leading them to break apart or dissolve into solutions, with their particles then being transported by wind or water, eventually forming sediments and other materials.
There are numerous minerals capable of experiencing chemical weathering, but each will decompose at different rates. According to the Goldich stability series, feldspar degrades more slowly than olivine and pyroxene.
Chemical weathering plays an essential role in plant life. By making minerals available to plants for absorption and use in growth processes, chemical weathering creates a vital cycle.
Chemical weathering processes can also pose geological threats. Wave action, for instance, can erode coastal cliffs by weakening their rock structure; chemical weathering causes rocks to crumble through processes such as iron corrosion. Therefore it is vital that we understand how these processes operate in order to safeguard ourselves against their impacts.
Biological
Biological weathering occurs when living organisms break down rock. This includes plants, fungi, bacteria and other microorganisms as well as animals digging or burrowing into rocks or soil to access nutrients for survival. Some forms of biological weathering also involve physical and chemical actions to break up rocks further.
Tree roots penetrate cracks and joints in rock to slowly break it apart mechanically, and also secrete organic acids which break down minerals in it. Lichens and mosses may alter its composition by exchanging ions for mineral nutrients found within its composition.
Humans contribute significantly to biological weathering through mining or quarrying rock and disturbing the ground’s surface, as well as foot traffic causing wear-and-tear that breaks off small pieces of rock, leading to longer term damage that often has devastating health impacts in historically marginalized communities. A combination of negative environmental factors may cause high blood pressure, diabetes, cardiovascular disease and poor mental health conditions to arise more readily than elsewhere.
Human
Burning fossil fuels releases gases into the atmosphere that, combined with moisture, form acids. These acids accelerate chemical weathering by weakening and disintegrating rock. Acid rain makes tombstone inscriptions hard to read because its acid dissolves the limestone and marble components used in their construction.
Socioeconomic disadvantage, political marginalization and racism can have devastating repercussions for one’s health, leading them to die prematurely. Dr. Geronimus compares this effect to playing Jenga: every block you remove causes its tower to crumble further down.
Her work has received much recognition, with research supporting her theory. For instance, one study recently discovered that Black women’s telomeres–the ends of DNA molecules–are shorter than white women, leading them to age more quickly and decrease life expectancy as well as suffer higher rates of cardiovascular disease, stroke, and diabetes.