In the warm, moist conditions of many burial environments, degradation can occur within centuries.

In exceptional cases — extreme cold, or extreme aridity, or specific chemical conditions that inhibit bacterial and chemical degradation — DNA can survive for much longer.

Denisova Cave’s cool, stable interior temperatures are one of the reasons ancient DNA has survived in the bone fragments recovered there.

The constant low temperature slows the chemical reactions that degrade DNA, preserving fragments of genetic information for far longer than would be possible in a warmer environment.

But even in exceptional preservation conditions, the DNA that survives is not intact.