The powder is then treated with chemical solutions designed to break down the remaining mineral structure and free the DNA it contains.

The result is a solution containing whatever DNA survived: a mixture of ancient endogenous sequences (the genuine ancient DNA of the tooth’s original owner), environmental DNA from organisms that colonized the tooth after death, and potentially modern contamination introduced during the extraction process.

Separating these components requires multiple steps.

The length distribution of the DNA fragments is informative: genuinely ancient DNA tends to be very short — fragments of 30 to 100 base pairs are typical, compared to the millions of base pairs in chromosomes of living cells.

Modern contamination typically consists of longer fragments.