Weathering, which refers to the process of the break down of rocks and minerals near Earth’s surface through chemical and physical means, also includes living or once-living organisms as potential aid in weathering rocks.
Water is one of the primary agents of weathering. It seeps into cracks in rock, seeping into spaces between it, and, if frozen, can force its way between cracks to push apart.
Water
Water is a key player in weathering. It erodes rocks and soil, both physically and chemically. Air pollution from fossil fuels can speed up weathering processes by mixing carbon dioxide with rainwater into acids which then return as acid rain and begin eating away at rocks.
Water contributes to physical weathering by expanding and contracting in cracks, which causes rocks to crumble apart and fracture into pieces, often leaving holes behind. Plants and animals also play an integral part of biological weathering by breaking it down through roots or trampling on it – processes known as biological weathering.
Ice
Ice is frozen water that forms solid forms when exposed to environmental conditions, and when present it can cause both physical and chemical damage to structures and materials.
Mechanical weathering relies heavily on liquid and frozen forms of water for its effectiveness in breaking apart rocks in climates with fluctuating temperatures above and below freezing.
Mechanical weathering processes that remove rock fragments include: abrasion, crystallization of ice, freeze-thaw cycles, hydration shattering and exfoliation. Each of these methods breaks down rocks but each uses slightly different strategies; together they work to sculpt Earth’s rocks before eventually washing them into the sea – depending on how long a rock has been exposed to these forces, its pace of wear-and-tear will depend on exposure time.
Acids
Chemical weathering involves changing rocks and minerals into something with different composition and physical attributes; this form of weathering often happens faster than physical weathering.
Acidic chemicals found in the air cause certain forms of weathering. For instance, nitrogen oxide and sulfur dioxide from burning fossil fuels react with sunlight and atmospheric water to form acids known as acid rain. Acid rain quickly wears away at limestone, marble, and other types of rock which then damage buildings, statues, or gravestones with writing that makes illegible over time.
Plants and fungi also produce acids, and these weak acids increase dissolution and change rates in their environment. Symbiotic mycorrhizal fungi of some trees secrete acids to aid their roots gain access to mineral-rich soils.
Salts
Salts are ionic compounds composed of multiple small ions bonded together into an ever-repeating three-dimensional structure. Salts have high melting and boiling points, are electrically conductive when melted or in solution and form crystal structures when solid.
Table salt (sodium chloride) is an example of pure salt. Composed of one sodium cation and one chlorine anion bound together firmly through repeated bonds, this compound forms white crystals when applied to snowy roadways. Rock salt helps lower water’s freezing point to deice snowy roadways more effectively than using plain salt alone due to melting ice faster. But below certain temperatures it becomes ineffective as deicer, so road crews sometimes also utilize calcium chloride to enhance its effectiveness at colder temperatures.
Plants
Plants help combat erosion by collecting rain through their leaves and branches, keeping it from blowing away while helping it absorb into the ground. Their roots may help weather rocks and soil by secreting organic acids or chelating molecules; bacteria in their roots may even release inorganic nutrients from minerals that boost plant growth.
Chemical and physical weathering work together to erode rock and soil. Water, ice, salts, acids, plants and temperature fluctuations all play an essential part of this process; no hard rock can resist its forces; over time these processes erode even tallest mountains into pieces which then get carried away by erosion.
Animals
Animals are highly attuned to changes in weather. When temperatures become extreme, they can become lethargic or seek shelter, sometimes even hibernating!
Animals that burrow or tunnel through rocks can also contribute to mechanical weathering – for instance a rabbit burrowing through rocks can enlarge existing cracks in them and eventually break them apart, helping the weathering process along.
Chemical weathering can be caused by animals and plants, but humans can accelerate it as well. For instance, burning fossil fuels releases chemicals which transform into acids before falling back down as rain as acid rain. This form of weathering quickly breaks down limestone and other forms of rock.