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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.
Carbon compounds are defined as chemical substances containing carbon. [1] [2] More compounds of carbon exist than any other chemical element except for hydrogen. Organic carbon compounds are far more numerous than inorganic carbon compounds. In general bonds of carbon with other elements are covalent bonds.
In the iron–carbon system (i.e. plain-carbon steels and cast irons) it is a common constituent because ferrite can contain at most 0.02wt% of uncombined carbon. [6] Therefore, in carbon steels and cast irons that are slowly cooled, a portion of the carbon is in the form of cementite. [ 7 ]
CI chondrites also have a high carbon content. Besides inorganic carbon compounds like graphite, diamond and carbonates, organic carbon compounds are represented. For instance, amino acids have been detected. This is a very important fact in the ongoing search for the origin of life.
Carbon's widespread abundance, its ability to form stable bonds with numerous other elements, and its unusual ability to form polymers at the temperatures commonly encountered on Earth enables it to serve as a common element of all known living organisms. In a 2018 study, carbon was found to compose approximately 550 billion tons of all life on ...
Some examples of minerals in iron-rich rocks containing oxides are limonite, hematite, and magnetite. An example of a mineral in iron-rich rock containing carbonates is siderite and an example of minerals in an iron-rich rock containing silicate is chamosite. [2] They are often interbedded with limestones, shales, and fine-grained sandstones.
The composition of the Earth changed after its formation due to loss of volatile compounds, melting and recrystalization, selective loss of some elements to the deep interior, and erosion by water. [3]: 55 The lanthanides are especially difficult to measure accurately. [4]
The oxidized form of iron can then be the electron acceptor for reduced sulfur, H 2, and organic carbon compounds. This returns the iron to the reduced Fe(II) state, completing the cycle. [32] The transition of iron between Fe(II) and Fe(III) in aquatic systems interacts with the freshwater phosphorus cycle.