As a result it is always undergoing natural radioactive decay while the abundances of the other isotopes are unchanged.Carbon-14 is most abundant in atmospheric carbon dioxide because it is constantly being produced by collisions between nitrogen atoms and cosmic rays at the upper limits of the atmosphere.Since the 1960s, scientists have started accounting for the variations by calibrating the clock against the known ages of tree rings. Radio carbon dating works on the principle of radioactive decay.Carbon dating is accurate up to roughly 50,000 years ago.After this the rate of decay is too small to get accurate dates from a sample, and other dating methods (such as Thermoluminescence and Potassium-Argon) have to be used. When something dies its body stops taking in carbon. Along with hydrogen, nitrogen, oxygen, phosphorus, and sulfur, carbon is a building block of biochemical molecules ranging from fats, proteins, and carbohydrates to active substances such as hormones.All carbon atoms have a nucleus containing six protons.
When isotopes are to be designated specifically, the chemical symbol is expanded to identify the mass (for example, C is not stable.
Ninety-nine percent of these also contain six neutrons.
The 6 proton 6 neutron atoms are said to have a mass of 12 and are referred to as "carbon-12." The nuclei of the remaining one percent of carbon atoms contain not six but either seven or eight neutrons in addition to the standard six protons.
The ratio of carbon-12 and carbon-14 are constant in a living organism.
However, no more carbon-14 is absorbed after the organism dies.