The nine to ten meters of permafrost that covered the cultural layer did not merely protect the stone tools and ivory artifacts.

It protected the molecular record embedded in the two milk teeth that lay among them — the record that, when finally read, named a lost population and connected it to the ancestry of millions of people on a different continent.

This is what permafrost preservation means in practice: information that would have decomposed in a warmer environment, that would have been lost to the chemistry of biological decay, survived because the temperature of the ground was below freezing.

The DNA in those teeth was not fresh — it was degraded, fragmented, mixed with contaminating material from the environment.