Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters. Weathering occurs in situ, or "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity.
Two important classifications of weathering processes exist – physical and chemical weathering; each sometimes involves a biological component. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. The second classification, chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals (also known as biological weathering) in the breakdown of rocks, soils and minerals.
The materials left over after the rock breaks down combined with organic material creates soil. The mineral content of the soil is determined by the parent material, thus a soil derived from a single rock type can often be deficient in one or more minerals for good fertility, while a soil weathered from a mix of rock types (as in glacial, aeolian or alluvial sediments) often makes more fertile soil. In addition many of Earth's landforms and landscapes are the result of weathering processes combined with erosion and re-deposition. Contents
Mechanical or physical weathering means the breakdown of rocks and soils through direct contact with atmospheric conditions such as heat, water, ice and pressure. Wind
Wind processes are called 'aeolian'. Wind erodes the Earth's surface by removing loose, fine-grained particles, called 'deflation'.
Wind carrying sand wears grinds down surfaces with its windbourne particles.
Regions which have intense and sustained erosion are called deflation zones. Most aeolian deflation zones are composed of desert pavement, a sheet-like surface of rock fragments that remains after wind and water have removed the fine particles. Almost half of Earth's desert surfaces are stony deflation zones. The rock mantle in desert pavements protects the underlying material from deflation. Rain
Rain is another force that works slowly. The force of raindrops on some rocks make them wear down. Rain also can make a chemical change in some rocks. The water mixes with the minerals in the rock to break it down. Temperature
Freeze-thaw weathering of a rock in southern Iceland
Changing temperature can make a rock crack. Every day when the sun shines on the rock, its surface is heated. Heat causes the surface to expand (get bigger) a little. The inside of the rock, though, does not heat up as fast as the outside of the rock. The inside of the rock stays cooler. At night, the surface cools down and contracts. The expanding and contracting makes some places on the surface weak, and a crack is made.
Also, if water gets into a crack in a rock and the temperature goes below the freezing point, the water will freeze and expand. After some time, the rock may be weak enough to break into pieces. Ice
Ice, which can be miles thick, grinds the surface of the rock below it. The particles are carried with the ice, and if a glacier ends up in the sea, so does all the material carried with it. Chemical weathering
Chemical weathering is the direct effect of atmospheric or biological chemicals in the breakdown of rocks, soils and minerals. Carbon dioxide cycle
The carbon dioxide cycle is the most important for weathering. CO2 is put into the atmosphere mostly by volcanoes, and it is taken out of the atmosphere by photosynthesis, and by one other process.
While it is in the air, CO2 can dissolve in water droplets to form dilute carbonic acid.
"Weathering is a large consumer of the atmospheric carbon dioxide essential for dissolving rocks".
In fact, since volcanoes have not been very...
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