Carbon dating cycle
C-12 is by far the most common isotope, while only about one in a trillion carbon atoms is C-14.
C-14 is produced in the upper atmosphere when nitrogen-14 (N-14) is altered through the effects of cosmic radiation bombardment (a proton is displaced by a neutron effectively changing the nitrogen atom into a carbon isotope).
Nitrogen atoms high in the atmosphere can be converted to radiocarbon if they are struck by neutrons produced by cosmic ray bombardment.
The rate of bombardment is greatest near the poles, where the Earth's magnetic field is dipping into the Earth and therefore does not deflect incoming cosmic rays.
It takes about 5,730 years for half of a sample of radiocarbon to decay back into nitrogen.
The production of radiocarbon has not varied wildly through time, but the changes produce consistent differences from calander ages. 3.5 decays/gram/minute of carbon would be produced by a sample 11,460 years old. However, atmospheric testing of nuclear weapons in the late 1950's and early 1960's greatly increased the amount of radiocarbon in the atmosphere, so the decay rate of 14 decays per minute more than doubled. Sign up for INFObytes and receive an MP3 (audio presentation) called Genesis, The Gospel and the Creation/Evolution Issue by Dr Emil Silvestru—free for you to download! This is how carbon dating works: Carbon is a naturally abundant element found in the atmosphere, in the earth, in the oceans, and in every living creature.
This can be overcome by calibration curves calculated by dating materials of precisely known age.