Oldest thing found carbon dating
From the moment we die the proportion of carbon-14 compared to non-radioactive carbon-12 in what's left of our bodies starts to drop as it gradually turns to nitrogen.
And the longer dead things lie around, the lower the carbon-14 levels get.
And nuclear reactions have seen a leap in carbon-14 activity since 1945.
Luckily for us we have a record of atmospheric carbon-14 levels for every one of the last 12,000 years.
The exact age of an unknown sample can never be known for sure, so short of discovering a time machine, 95 per cent accuracy is as good as it gets.
As well as the tree ring record, scientists have used the carbon record from corals to calculate C14/C12 levels right back to 50,000 years ago.By about 58,000 years (ten half-lives) after an organism has died, there's so little radioactive carbon left (less than 1/1000) that calculations of age are no longer accurate.That's why radiocarbon dating is only reliable for samples up to 50,000 years old.It's not that the radioactive carbon in air or food doesn't decay, it does.
But something else is going on that keeps producing new carbon-14 — otherwise it would have all turned to nitrogen millions of years ago.
But old age isn't the only thing that affects the accuracy of carbon dating.