Carbon 14 dating is reliable for rocks that are
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.
Radiocarbon dating has somehow avoided collapse onto its own battered foundation, and now lurches onward with feigned consistency.
The implications of pervasive contamination and ancient variations in carbon-14 levels are steadfastly ignored by those who base their argument upon the dates.
Their results were 'two to three times less accurate than implied by the range of error they stated.' They thought the variations might have been caused by poor laboratory standards allowing contamination of the samples.
Some scientists believe the problem runs far deeper than this, as the following quote shows: In the light of what is known about the radiocarbon method and the way it is used, it is truly astonishing that many authors will cite agreeable determinations as "proof" for their beliefs...
They found large variations in the radiocarbon 'dates' of objects of known age sent to 38 radiocarbon 'dating' laboratories around the world.
Only one out of every trillion carbon atoms is C14. The C14 created in the upper atmosphere reacts with oxygen to become carbon dioxide.
Usually a proton is knocked out of the nitrogen atom's nucleus and is replaced with the neutron.
The proton takes an electron with it and becomes an atom of hydrogen.
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.