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This limit is currently accepted by nearly all radiocarbon dating practitioners.

It follows that the older a date is, even within this 'limit', the greater are the doubts about the date's accuracy.

The nitrogen atom, which began with seven protons and seven neutrons, is left with only six protons and eight neutrons.

As the number of protons decides the chemical nature of an atom, the atom now behaves like a carbon atom.

The carbon dioxide is absorbed by plants, and the plants are eaten by animals, thus contaminating every living thing on earth with radioactive carbon. As time passes, the C14 in its tissues is converted back into nitrogen.

If we know what the original ratios of C14 to C12 were in the organism when it died, and if we know that the sample has not been contaminated by contact with other carbon since its death, we should be able to calculate when it died by its C14 to C12 ratio.

This method is claimed to be more accurate than the older and slower method of counting the number of radioactive decay emissions from a quite large sample.

But in actual practice, we know neither the original ratios nor if the specimen has been contaminated and are forced to make what we hope are reasonable assumptions.

The tiny initial amount of C14, the relatively rapid rate of decay (the half-life of C14 is currently about 5700 years) and the ease with which samples can become contaminated make radiocarbon dating results for samples "older" than about 50,000 years effectively meaningless.

...[Some authors have said] they were "not aware of a single significant disagreement" on any sample that had been dated at different labs.

Such enthusiasts continue to claim, incredible though it may seem, that "no gross discrepancies are apparent".

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