concept

Ancient DNA

DNA surviving in ancient remains, and its limit is a hard number rather than a technical problem. Water cleaves DNA by two routes - depurination and deamination - so it decays with first-order kinetics. Allentoft and colleagues measured 158 dated moa bones and found a half-life of about 521 years for a 242-base fragment at 13 °C. Because the rate is Arrhenius-dependent on temperature, the theoretical ceiling is roughly 1 to 1.5 million years in permafrost, and under 150,000 years in the tropics. Dinosaur DNA is therefore a chemical impossibility.