The flooding that filled the cave with water had occurred after her death — sometime in the early Holocene, as the glaciers melted and sea levels rose, raising the water table beneath the Yucatán Peninsula until it overtook the air-filled cave system.

The bones had been sitting in water for most of the twelve thousand years since the cave flooded, preserved by the specific chemistry of the cave water — its consistent temperature, its mineral content, and the absence of the organic acids that destroy bone in most terrestrial burial environments.

It was one of those improbable chains of preservation that periodically delivers something from the deep past that should not have survived.

Why Scientists Needed The DNA