Radiocarbon dating age of the earth
...[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".As you might guess, radioactive carbon (C) is quite rare.Only one out of every trillion carbon atoms is C14. The C14 created in the upper atmosphere reacts with oxygen to become carbon dioxide.
It uses accelerator mass spectrometry to determine the amounts of C14 and C12 in a small sample which is vaporised in the test.It is the supposed accuracy of the new method that allows measurements sensitive enough to date objects claimed to be more than twenty or thirty thousand years old.A recent test by the British Science and Engineering Research Council has shown that the accuracy of the new technique is greatly overrated.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.
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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.