Radioactive isotopes used in carbon dating
As stated previously, carbon dating cannot be used on artifacts over about 50,000 years old.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.The mathematical premise undergirding the use of these elements in radiometric dating contains the similar confounding factors that we find in carbon-14 dating method.
Also, many fossils are contaminated with carbon from the environment during collection or preservation procedures.
Nuclear tests, nuclear reactors and the use of nuclear weapons have also changed the composition of radioisotopes in the air over the last few decades.
This human nuclear activity will make precise dating of fossils from our lifetime very difficult due to contamination of the normal radioisotope composition of the earth with addition artificially produced radioactive atoms.
Levels of carbon-14 become difficult to measure and compare after about 50,000 years (between 8 and 9 half lives; where 1% of the original carbon-14 would remain undecayed).
The question should be whether or not carbon-14 can be used to date any artifacts at all? There are a few categories of artifacts that can be dated using carbon-14; however, they cannot be more 50,000 years old.