While the small variations in isotope decay that have been reported may not invalidate all isotopic dating, they raise questions about the assumption of completely uniform decay rates.A second assumption is that the sample being dated has not experienced any loss or contamination of C over its history.In most cases, the three methods produced similar results.
Three additional assumptions are necessary in radiocarbon dating in order to estimate the initial concentration of C could be caused by changes in the intensity of the cosmic radiation or in the strength of the earth’s magnetic field.
Carbon-14 dating cannot be applied to materials that have no C dates are less than that figure.
It is sometimes thought possible to extend the dating range a few half-lives, so one occasionally sees dates as old as 70,000 years or more.
Other processes may affect the local concentrations of carbon-14.
These effects are corrected for by comparing samples from different locations.