Dendrochronology, the study of tree-time, is a multidisciplinary science that provides chronometric, environmental, and behavioral data to archaeologists and other scientists.
Tree-ring dating is, unfortunately, not universally applicable.
Thus by comparing the relative quantity of carbon -12 and carbon -14 in an organic matter excavated scientists can predict the age of the object (R. Where N is the current amount, N_o is the original amount, lambda is the proportionality constant for the growth rate (which is negative for decay), and t is the amount of time that has passed. Source: (Brain, 2014) The half-life of carbon-14 is 5730 years.
This implies that it takes 5730 years for half of the 14C atoms in the organic matter to get decayed.
When an organism is dead the intake of the carbon-14 stops and in a 5730 year time period, half of the amount of carbon-14 present in the organic matter would have undergone beta decay to form stable Nitrogen-14.