text: how long is radiactive carbon dating approx. useful for?   carbon-14 radioisotopic dating is only good for a range backward about 60,000 years, +/- 5,000 years. that means that it is only good for archaeology, from modern to prehistoric man, and extremely recent paleontology, such as mammoth bones and sabre-toothed cats. for beyond 60,000 years, either potassium-40 or uraniums' -238 and -235 are used.