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So, if we find the remains of a dead creature whose C-12 to C-14 ratio is half of what it's supposed to be (that is, one C-14 atom for every two trillion C-12 atoms instead of one in every trillion) we can assume the creature has been dead for about 5,730 years (since half of the radiocarbon is missing, it takes about 5,730 years for half of it to decay back into nitrogen).If the ratio is a quarter of what it should be (one in every four trillion) we can assume the creature has been dead for 11,460 year (two half-lives).
C-12 is by far the most common isotope, while only about one in a trillion carbon atoms is C-14.By measuring radioactive carbon-14 deposited in tusks and teeth following open-air nuclear bomb tests, the method reveals the year an animal died, and thus whether the ivory was taken illegally."This could be used in specific cases of ivory seizures to determine when the ivory was obtained and thus whether it is legal," said University of Utah geochemist Thure Cerling, senior author of the study.The amount of cosmic rays penetrating the earth's atmosphere is itself affected by things like the earth's magnetic field which deflects cosmic rays.Precise measurements taken over the last 140 years have shown a steady decay in the strength of the earth's magnetic field.
And yet we know that "radiocarbon is forming 28-37% faster than it is decaying," which means it hasn't yet reached equilibrium, which means the ratio is higher today than it was in the unobservable past.