Carbon-14 has a half-life of 5,730 years. That means that no matter how many carbon-14 atoms were present when something died, after 5,730 years only half of them are left — the rest have decayed to nitrogen. Thats why radiocarbon dating is only reliable for samples up to 50,000 years old.
Why cant carbon dating be used for ages 50000 years and older?
Carbon dating also 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.
Why is carbon-14 useful only for dating events less than about 50000 years ago?
Carbon dating only works for objects that are younger than about 50,000 years, and most rocks of interest are older than that. Carbon-14 has a half life of 5730 years, meaning that 5730 years after an organism dies, half of its carbon-14 atoms have decayed to nitrogen atoms.