But how long does that take? A new calculation by paleogeneticists Morten Allentoft at the University of Copenhagen and Michael Bunce at Murdoch University in Perth, based on DNA from 158 leg bones of extinct Moa (giant birds), 600 to 8,000 years old, says that the half life of the nucleotide bonds in DNA is 521 years. That is, after 521 years, half the bonds have decayed, and so on:
The team predicts that even in a bone at an ideal preservation temperature of −5 ºC, effectively every bond would be destroyed after a maximum of 6.8 million years. The DNA would cease to be readable much earlier — perhaps after roughly 1.5 million years, when the remaining strands would be too short to give meaningful information.However, this is not a nuclear process like the decay of Carbon 14, but a chemical process influenced by the environment. In very dry or very cold conditions, the rate might be much slower; how much slower, nobody knows. Conversely, in the warm, alternating wet-and-dry conditions of the average European or North American archaeological site, the rate might be faster.
“This confirms the widely held suspicion that claims of DNA from dinosaurs and ancient insects trapped in amber are incorrect,” says Simon Ho, a computational evolutionary biologist at the University of Sydney in Australia. However, although 6.8 million years is nowhere near the age of a dinosaur bone — which would be at least 65 million years old — “We might be able to break the record for the oldest authentic DNA sequence, which currently stands at about half a million years,” says Ho.