carbon-12

isotope

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June 23, 2026

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Carbon-12 is a stable isotope of carbon, meaning it does not undergo radioactive decay. It is the most abundant isotope of carbon, making up about 98.93% of natural carbon.12

Carbon-12 is used as a standard for measuring atomic weights. Its atomic mass is defined as exactly 12 atomic mass units (amu). The notation for this isotope is ¹²₆C.132

While carbon-12 and carbon-13 are stable isotopes, carbon also has radioactive isotopes, the most well-known being carbon-14, which has a half-life of approximately 5,730 years and is used in radiocarbon dating. Carbon-12 plays a role in the CNO cycle, a process of energy creation in certain stars.2

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atomic mass unit
…of a single atom of carbon-12, the most abundant isotope of carbon, or 1.660538921 × 10⁻²⁴ gram. The mass of an atom consists of the mass of the nucleus plus that of the electrons, so the atomic mass unit is not exactly the same as the mass of the…
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…of a single atom of carbon-12, the most abundant isotope of carbon, or 1.660538921 × 10⁻²⁴ gram. The mass of an atom consists of the mass of the nucleus plus that of the electrons, so the atomic mass unit is not exactly the same as the mass of the…
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Permian extinction
Alteration of the carbon cycle
…unusually high amounts of ¹²C trapped in Permian sediments to be a result of widespread oceanic anoxia (very low levels of dissolved oxygen). They associate this anoxia with the prolonged eruption of the Siberian flood basalts (the so-called Siberian Traps), which probably led to higher levels of carbon dioxide…
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…unusually high amounts of ¹²C trapped in Permian sediments to be a result of widespread oceanic anoxia (very low levels of dissolved oxygen). They associate this anoxia with the prolonged eruption of the Siberian flood basalts (the so-called Siberian Traps), which probably led to higher levels of carbon dioxide…
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carbon
In 1961 the isotope carbon-12 was selected to replace oxygen as the standard relative to which the atomic weights of all the other elements are measured. Carbon-14, which is radioactive, is the isotope used in radiocarbon dating and radiolabeling.
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In 1961 the isotope carbon-12 was selected to replace oxygen as the standard relative to which the atomic weights of all the other elements are measured. Carbon-14, which is radioactive, is the isotope used in radiocarbon dating and radiolabeling.
Read More