carbon-12

…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…

…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…

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.