The tooth at the center of this story deserves its own moment of attention — not as a metaphor or a symbol, but as a physical object with specific properties that made the discovery possible.

Human teeth are composite structures.

The outer shell of enamel — the hardest substance the human body produces — is formed from tightly packed hydroxyapatite crystals arranged in a structure that is both rigid and resistant to biological degradation.

Enamel contains no living cells after it forms, which means it cannot be invaded or repaired by biological processes.

Once formed, it persists.

Beneath the enamel is dentin — a harder-than-bone material that forms the body of the tooth and that does contain cellular remnants.