With this said, it would be worth while to check out this feedback session which does seem to suggest that there might have been an accelerated decay rate in the past, at least for the uranium-lead method.
“It is important to realize that an accurate radiometric date can be obtained only if the mineral remained a closed system during the entire period since its formation.
Since C-14 is so well distributed in the atmosphere, it is assumed the same ratio that is in the atmosphere will also be in an organism.
Rather I am conceding due to no current evidence for the contrary).
But, as C-14 continuously decays, it is also continuously being replaced by new C-14 being formed.
How carbon-14 enters an organism Most C-14 will combine with oxygen to produce radioactive carbon dioxide (C-14 O-2).
After about 8 half-lives, the remaining amount of C-14 (if there is any remaining) is too small to be measured.
For this reason, it is simply impossible for carbon dating to give dates as old as millions of years. Closed systems, void of any contamination and without loss of the parent element (C-14) or daughter element. Known amounts of parent and daughter elements present from the beginning. If the decay rate of C-14 were not always constant, then this would be devastating to the technique's credibility.
Instead, it can only give up to approximately 50,000 years. Unfortunately, dating methods such as the carbon dating method have only been around for a short period of time.