It needs to be answered: How did Carbon-14 end up in diamonds?
http://www.icr.org/article/diamonds-may-be-creationists-best-friend
“Simultaneously during the RATE project, John Baumgardner discovered that diamonds contain measurable concentrations of carbon-14 that date them at less than 50,000 years, assuming conventional concentrations of atmospheric carbon-14 when they were formed. The question naturally arose—what was the source of the carbon-14?”
That is easily answered by the fact that the environment has a lot of carbon 14 and it constitutes background “noise” that is corrected for in radiometric testing. Carbon 14 testing in once living samples is not accurate and thus not usable beyond 50,000 years.