Radiocarbon dating was invented in the 1950s by the American chemist Willard F.Libby and a few of his students at the University of Chicago: in 1960, he won a Nobel Prize in Chemistry for the invention.Once an organism dies, it stops taking in carbon-14.
The raw radiocarbon date of any sample can then be converted to true date by using this calibration table.
The starting ratio of radiocarbon to stable carbon is locked in at that point. The purpose in each of these methods is to determine the ratio of radiocarbon to stable carbon in the sample.
From then on, the ratio of radiocarbon to stable carbon will decrease, because the unstable radiocarbon atoms will slowly decay. From this measurement the age in radiocarbon years is calculated. Modern radiocarbon dates are calibrated using long tree-ring chronologies.
The atmosphere contains many stable carbon atoms and relatively few radiocarbon atoms.
The ratio of radiocarbon to stable carbon atoms in the atmosphere has varied in the past.