The preservation of arecoline traces in 25,000-year-old dental tissue is not obvious, and understanding why teeth are such good chemical archives is important for appreciating the significance of the detection.

Tooth enamel is the hardest biological material in the human body.

It is primarily composed of hydroxyapatite — a calcium phosphate mineral — organized into a highly ordered crystalline structure.

This mineral composition makes enamel extraordinarily resistant to degradation: it survives in the archaeological record far better than bone, which contains more organic material and degrades more readily.

Within the enamel and the underlying dentine, organic compounds from the mouth can become incorporated during life.

This incorporation happens through several mechanisms: direct diffusion of compounds from saliva into the mineral matrix, binding of organic molecules to the hydroxyapatite crystal surface, and incorporation of compounds that precipitate from solution within the tooth structure.