A unique characteristic of 14C is that it is constantly formed in the atmosphere.Production and decay 14C atoms are produced in the upper atmosphere where neutrons from cosmic rays knock a proton from nitrogen-14 atoms.All radiocarbon laboratories either standardize to the US National Bureau of Standards Oxalic Acid I (OX-I) which is derived from Sugar Beets in 1955 or a secondary standard NBS OX-II (grown in 1977) or Australian National University Sucrose (ANU), which is sugar from the 1974 growing season in Australia.
This means that it can be difficult to effectively clean the samples and remove enough contaminating carbon to obtain an accurate date.
In the late 1970s and early 1980s the dating of small samples became possible using Accelerator Mass Spectrometry (AMS; Muller, 1977; Nelson et al., 1977).
When a plant or animal dies it no longer exchanges CO with the atmosphere (ceases to take 14C into its being). 14C decays by emitting an electron, which converts a neutron to a proton, converting it back to its original 14N form.
The History of Radiocarbon Dating Willard Libby invented radiocarbon dating in the late 1940s.
The age of known artefacts from Egypt were too young when measured by radiocarbon dating.