Carbon 14 dating system definition
In the northern hemisphere the amount of artificial carbon in the atmosphere reached a peak in 1963 (in the southern hemisphere around 1965) at about 100% above normal levels.
Since that time the amount has declined owing to exchange and dispersal of C14 into the Earth's carbon cycle system.
The effect of this has been to almost double the amount of C14 activity in terrestrial carbon bearing materials (Taylor, 1987).
De Vries (1958) was the first person to identify this 'Atom Bomb' effect.
The logical conclusion from this was that in order to obtain a modern radiocarbon reference standard, representing the radiocarbon activity of the 'present day', one could not very well use wood which grew in the 1900's since it was affected by this industrial effect.
Thus it was that 1890 wood was used as the modern radiocarbon standard, extrapolated for decay to 1950 AD.
In order to ascertain the ages of samples which were formed in equilibrium with different reservoirs to these materials, it is necessary to provide an age correction.
Similarly, this effect has been noted for plants in the bay of Palaea Kameni near the prehistoric site of Akrotiri, which was buried by the eruption of the Thera volcano over 3500 years ago (see Weninger, 1989).
[A Conventional Radiocarbon Age or CRA, does not take into account specific differences between the activity of different carbon reservoirs.