In cold, dry, sealed environments — conditions that slow or halt the biological and chemical processes of degradation — DNA can survive for an extraordinarily long time.

Some of the oldest ancient DNA ever successfully recovered comes from permafrost in Siberia and Canada, where the permanently frozen ground has preserved genetic material for hundreds of thousands of years.

The Spirit Cave environment was not permafrost, but the consistent aridity of the cave created conditions favorable to DNA preservation.

The question was whether those favorable conditions had been sufficient to preserve genetic material in recoverable form across more than ten thousand years.

To answer that question, Willerslev’s team extracted powder from the petrous bone — which, being the densest bone in the human body, provides some protection for the DNA within it — and applied next-generation sequencing technology.