![]() Ultimately, over millions of years, geologic changes in the uplift of land, driven by plate tectonics, alter the geographic location and amount of rock exposed for weathering.Evidence of weathering can be seen in the form of scattered piles of broken rock at the base of sheer cliff faces at Scotts Bluff National Monument. Additionally, regional soil quality, nutrient levels (especially nitrogen and phosphorus levels), are dependent on the type of rock that is weathered, which in turn affects local biodiversity. The weathering of rocks affects how much and what kind of rock is eroded by water, ice, wind, and gravity, which can affect soil formation, and where various sedimentary rocks form over thousands to millions of years. Visit the carbon and rock cycle pages to learn more about how weathering is connected to other Earth system processes. This rate is so high that even though the warming produced by the increased CO 2 increases the rate of weathering of silicate rocks, which draws down atmospheric CO 2, is not nearly enough to offset the increase in carbon dioxide added to the atmosphere by human activities. The burning of fossil fuels returns carbon to the atmosphere (as CO 2) at a rate that is hundreds to thousands of times faster than it took to bury. In contrast, the weathering of limestone by carbonic acid releases carbon dioxide into the atmosphere, but there is no net removal of CO 2 from the atmosphere as happens with the weathering of silicate rocks. This weak acid reacts with rocks, breaking them down, resulting in the transport of carbon via rivers to the ocean, where it ultimately becomes buried in ocean sediments to become limestone rock. Over long-time scales, significant amounts of carbon dioxide (a greenhouse gas) are removed from the atmosphere when rainwater (H 2O) mixes with CO 2 to form carbonic acid (H 2CO 3). Over thousands to many millions of years, the weathering of silicate rocks on land (rocks made of minerals that contain the element silica) is an important part of the carbon cycle. Plant growth, aside from physically breaking up rocks, can also change the environmental chemistry (for example, increase acidity) contributing to chemical weathering. The rate of these chemical reactions is affected by climatic conditions such as precipitation and temperature, with water and warmer temperatures increasing the rate. Additional causes of physical weathering include the freezing and expansion of water in rock cracks, and tree roots that dig into rocks that can split them apart.Ĭhemical weathering occurs when the breakdown of rock results from chemical change in the rock, or the when the rock is dissolved away. For example, physical weathering can happen as the temperature changes, causing rocks to expand as they warm and contract as they cool, resulting in cracks that lead to the breakdown of the rock. Physical weathering is the breakdown of rock into smaller pieces without altering the chemical composition of the rock. ![]() The weathering of rocks occurs through both physical and chemical processes. ![]() Credits: Wikipedia (top) and USGS (bottom) Bottom: The weak acid that results from CO2 dissolving in rainwater slowly dissolves limestone, here leaving to a honeycomb pattern in the limestone rock (bottom). Top: The weathering of granite, a rock rich in silicate minerals, crumbles the once hard rock into sand.
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