Weathering wears away at Earth’s rock layers by mechanical, chemical and biological processes.
Carbonic acid in rainwater, for instance, can dissolve limestone from Earth’s surface to form a karst landscape punctuated by caves.
Oxygen in air can also weaken rocks by reacting with iron to form compounds like rust. This process, known as chemical weathering, has long been practiced by geologists.
Water in rain, rivers and lakes can corrode rocks through freezing and thawing cycles, breaking apart rocks into pieces – this process is known as mechanical weathering.
Chemical weathering can also have an impact on rocks. When certain minerals react with oxygen and other chemicals to alter or dissolve their shapes or dissolve away altogether. Acid rain, for instance, erodes limestone and marble carvings so their carvings become unreadable while it also breaks down silicate minerals found in sedimentary rocks into clays.
Erosional activity can transport rocks to different areas where they are deposited in an act known as deposition. One such example of this process can be seen at work in the Grand Canyon, which was formed over centuries by erosion carried along by Colorado River waters and where deposition may have brought chemical pollutants from faraway locations.
Ice is a powerful agent in helping rocks weather, as it can enter cracks in rocks and expand them by freezing, known as freeze-thaw weathering or cryofracture. This process causes wedge effects in cracks which eventually fracture apart rock layers – something we see often enough with road crews fixing cracks along sidewalks or roads.
Water that freezes expands by about 10%, exerting outward pressure against rocks, known as mechanical weathering and potentially leading to fractured stones.
Wind can also alter rock by gradually wearing away particles of sand or stone over time, through erosion. As part of its process, erosion transports these worn-away rocks to other places where they become sediment deposited (deposited). This phenomenon is called sedimentation.
Wind is an influential force when it comes to weathering rocks, with its force able to wear away and break rocks as it transports their fragments from one place to the next. Furthermore, winds can bring about chemical changes within rocks which cause further weathering processes to take place.
Biological weathering refers to the process by which organisms such as lichen, fungi and algae alter the natural composition of rocks in order to make them easier for biological action to decompose and break apart.
Chemical weathering refers to the process by which rocks are worn away by chemical reactions, often due to acid rain produced when rainwater mixes with air pollutants.
Chemical weathering occurs when iron in rocks combines with oxygen to form compounds like rust. This causes it to become brittle and easier for it to break apart, or when silicate minerals decay into clay minerals and turn brittle over time.
Some plants, like mosses and mycorrhizal fungi that connect tree roots to their host trees, can help mechanically weather rocks. When these fungi grow into cracks in rocks, they widen them over time until eventually the rocks break apart completely.
Plants also play a part in chemical weathering. When they break down rocks and minerals, plants release chemical compounds which alter the molecular structure of rocks and when combined with water they form acidic substances which weaken and dissolve their material.
Fossil fuels release oxides of sulphur, carbon and nitrogen into the atmosphere which can make rainwater acidic, leading to acidification of limestone, marble and other rocks. Over time this acid rainwater may dissolve these rocks slowly.
Animals that do not hibernate or become dormant during cold weather must adapt to large fluctuations in temperature. These animals often struggle to find food & shelter during extreme weather events. Larger creatures who live longer tend to better withstand weather events while also producing many offspring over their lifespans.
Biological weathering occurs when living or once-living organisms wear away at rock. For instance, roots growing into cracks in rocks may eventually widen them over time.
Air pollution hastens weathering processes. Burning fossil fuels such as coal, natural gas and oil releases chemicals into the air that alter molecular structures in water to cause acid rain that eats away at rocks & soil.