Carbon dating and the
Plants and animals naturally incorporate both the abundant C-12 isotope and the much rarer radiocarbon isotope into their tissues in about the same proportions as the two occur in the atmosphere during their lifetimes.When a creature dies, it ceases to consume more radiocarbon while the C-14 already in its body continues to decay back into nitrogen.This man-made fluctuation wasn't a natural occurrence, but it demonstrates the fact that fluctuation is possible and that a period of natural upheaval upon the earth could greatly affect the ratio.Volcanoes spew out CO which could just as effectively decrease the ratio.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).The new isotope is called "radiocarbon" because it is radioactive, though it is not dangerous.It takes another 5,730 for half of the remainder to decay, and then another 5,730 for half of what's left then to decay and so on.The period of time that it takes for half of a sample to decay is called a "half-life."Radiocarbon oxidizes (that is, it combines with oxygen) and enters the biosphere through natural processes like breathing and eating.
We also know that the ratio decreased during the industrial revolution due to the dramatic increase of CO produced by factories.
It is naturally unstable and so it will spontaneously decay back into N-14 after a period of time.