Its specific density derives from the extremely compact arrangement of its mineral crystals — a structural adaptation that evolved to protect the delicate sensory apparatus of the inner ear from vibration and mechanical disturbance.

This same density makes the petrous bone dramatically more resistant to the processes that degrade other bones: microbial penetration, chemical dissolution, and the physical disturbances of burial are all less effective against the petrous bone than against the more porous bones of the rest of the skeleton.

Inside the petrous bone’s dense mineral structure, pockets of ancient DNA can be preserved even when the bone’s organic content has otherwise been substantially depleted by diagenesis — the chemical and biological processes that transform buried materials over time.

The specific chemical environment within the mineral matrix protects DNA fragments from the enzymatic and chemical degradation that consumes them in other contexts.