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A group of hikers encountering quicksand on the banks of the Paria River, Utah Quicksand warning sign near Lower King Bridge, Western Australia. Quicksand is a shear thinning non-Newtonian fluid: when undisturbed, it often appears to be solid ("gel" form), but a less than 1% change in the stress on the quicksand will cause a sudden decrease in its viscosity ("sol" form).
Schematic representation of the overall perturbation of the global carbon cycle caused by anthropogenic activities, averaged from 2010 to 2019. [1] The atmospheric carbon cycle accounts for the exchange of gaseous carbon compounds, primarily carbon dioxide (CO 2), between Earth's atmosphere, the oceans, and the terrestrial biosphere.
In a given year between 10 and 100 million tonnes of carbon moves around this slow cycle. This includes volcanoes returning geologic carbon directly to the atmosphere in the form of carbon dioxide. However, this is less than one percent of the carbon dioxide put into the atmosphere by burning fossil fuels. [2] [32] [37]
The carbon cycle is a biogeochemical cycle that is important in maintaining life on Earth over a long time span. The cycle includes carbon sequestration and carbon sinks . [ 4 ] [ 5 ] Plate tectonics are needed for life over a long time span, and carbon-based life is important in the plate tectonics process. [ 6 ]
The carbonate-silicate cycle is the primary control on carbon dioxide levels over long timescales. [3] It can be seen as a branch of the carbon cycle, which also includes the organic carbon cycle, in which biological processes convert carbon dioxide and water into organic matter and oxygen via photosynthesis. [5]
Carbon is returned to the atmosphere via volcanic gases. Carbon undergoes transformation in the mantle under pressure to diamond and other minerals, and also exists in the Earth's outer core in solution with iron, and may also be present in the inner core. [1] Carbon can form a huge variety stable compounds.
A major part of carbon dioxide emissions dissolved in water and reacted with metals such as calcium and magnesium during weathering of crustal rocks to form carbonates that were deposited as sediments. Water-related sediments have been found that date from as early as 3.8 billion years ago.
In Earth's atmosphere, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle. It is one of three main greenhouse gases in the atmosphere of Earth. The concentration of carbon dioxide (CO 2) in the atmosphere reached 427 ppm (0.04%) in 2024. [1]