Scientists attempt to check the accuracy of carbon dating by comparing carbon dating data to data from other dating methods.
Other methods scientists use include counting rock layers and tree rings.
The age of the carbon in the rock is different from that of the carbon in the air and makes carbon dating data for those organisms inaccurate under the assumptions normally used for carbon dating.
These artifacts have gone through many carbon-14 half-lives, and the amount of carbon-14 remaining in them is miniscule and very difficult to detect.
When scientists first began to compare carbon dating data to data from tree rings, they found carbon dating provided "too-young" estimates of artifact age.
Scientists now realize that production of carbon-14 has not been constant over the years, but has changed as the radiation from the sun has fluctuated.
Carbon-14 cannot be used to date biological artifacts of organisms that did not get their carbon dioxide from the air.
This rules out carbon dating for most aquatic organisms, because they often obtain at least some of their carbon from dissolved carbonate rock.