Weathering, or the slow breakdown of rocks and minerals on Earth’s surface caused by physical and chemical processes like rainwater, ice melt, acids, salts, plants/animals living nearby and changes in temperature all play an essential part.
Plant roots that grow into cracks in rocks cause the crack to widen – this is an example of mechanical weathering.
Physical weathering refers to the breakdown of rocks and minerals by mechanical means. Even massive rocks crack along naturally weak areas like bedding planes in sedimentary rocks, exfoliation surfaces in metamorphic rock or fractures in massive igneous rocks; cracks created by physical weathering allow chemical or biological weathering processes to widen them further.
Water is one of the primary agents of mechanical weathering. It has the capacity to dissolve various types of rock, such as some sandstones. Furthermore, its freezing and expanding capabilities enable it to find its way into small cracks in rock surfaces, where plant roots may cause the cracks to widen further before eventually breaking them open entirely.
Acids in the atmosphere may contribute to weathering. Sulfur dioxide, nitrogen compounds and carbon dioxide react with water in the air to form acids which fall to Earth as raindrops, often stripping essential chemicals from minerals found within rocks.
Chemical weathering refers to any change that results from interactions between minerals and their surroundings at the surface. Minerals which were once stable under higher pressures and temperatures within Earth’s crust become unstable when exposed to lower temperature/lower pressure conditions at its surface; their molecular structures no longer match up well with what exists there.
Silicate minerals found in igneous rocks such as quartz and K, Na-rich feldspar decay over time along crystal boundaries into clays through Bowen’s reaction series.
Chemical weathering includes the breakdown of rock by water to produce clay minerals and soluble salts (hydrolysis) or iron-rich rocks by oxygen in an oxidation process that gives them a reddish brown appearance (rust), commonly resulting in what’s commonly referred to as shale. Plants also play an integral part in weathering processes both mechanical and chemical. Tree roots can enlarge cracks in rocks while animals that tunnel underground or dig and trample aboveground can break apart both rocks and soil.
Plants and microorganisms (such as fungi) can aid the process of chemical weathering by changing the environment of rocks they come into contact with. Acid-producing roots, for instance, may aid the breakdown of rock by solubilizing minerals or releasing ligands that complex with metals in its structures; while fungi release chemicals that break down minerals or form cracks or holes. Furthermore, lichen (a symbiotic relationship between fungi and algae) produces chemicals that weaken and dissolve rock; releases chemicals which weaken and dissolve it further.
Animals that burrow through soils or dig for food can hasten biological weathering by bringing rock fragments closer to the surface where they can be exposed to additional mechanical and chemical weathering processes. Humans too can hasten this form of weathering by planting trees or simply walking and running, activities that disrupt the earth’s surface.
Humans contribute to weathering processes by both biological and mechanical means. Physical biotic weathering occurs when living organisms exert pressure upon rocks that causes changes to occur through physical contact – for instance a bird pecking at it or humans digging it up or breaking it apart.
Carbon dioxide gas created from burning fossil fuels enters the atmosphere, mixing with water and producing acid rain that accelerates chemical weathering of rocks and minerals by attacking their surfaces.
Stress caused by racism, prejudice and income inequality can hasten biological aging through an increase in cortisol and testosterone production – known as biological aging and leading to health conditions like high blood pressure, diabetes and obesity. To counteract its negative impacts, one must address structural inequalities and systemic racism at their source.