The Arctic changes those calculations significantly. The cold temperatures that make the Arctic so lethal to unprepared humans also dramatically slow the chemical processes of decomposition. Cold temperatures slow enzymatic activity, reduce the reactivity of DNA with its environment, and prevent the proliferation of the microorganisms — bacteria and fungi — that consume organic material and produce metabolic acids that attack DNA. For biological material in an Arctic environment, decomposition happens, but it happens much more slowly than it would in warmer conditions.
But temperature alone is not enough to explain why a tooth from an 1848 expedition site could yield usable DNA in 2024. The physical structure of a tooth matters as much as the environmental conditions.
A tooth is, in structural terms, a remarkable package. The outer surface of the crown — enamel — is the hardest biological material the human body produces. Enamel is composed almost entirely of hydroxyapatite, a calcium phosphate mineral, with minimal organic content. It is extremely resistant to the chemical and mechanical processes that break down soft tissue. Beneath the enamel lies dentin — also mineralized, though less so than enamel — which forms the bulk of the tooth’s structure. At the center of the tooth is the pulp cavity, containing the soft tissue of the pulp and the root canal system extending through the roots.
The DNA in a tooth is not in the enamel, which contains almost none. It is in the cellular material of the pulp and in the dentin itself, which contains tubules lined with cells. These cellular materials are physically enclosed within the dentin shell and the enamel shell on top of it, creating a barrier between the DNA-containing material and the outside environment. When a tooth is separated from the body after death, these barriers persist. The enamel and dentin continue to protect the interior from the environmental agents — bacteria, moisture, oxygen — that would otherwise attack the genetic material.