Grim discovery sheds new light on when humans came to the Americas

She was young, no more than 16, and feeling her way through a dark cave, perhaps lured by the quest for water in a land with no surface rivers or streams.

One can imagine her terror as the cave suddenly opened into a yawning chasm, with a sheer drop to a shallow pool far below. A step too far took her over the unseen edge. In pitch blackness she fell as much as 30 metres about eight storeys. The echoes of her scream and the sound of her body as it hit bottom would have echoed off the limestone walls for a few moments. Then eons of silence.

Globe and Mail Update May. 15 2014, 2:27 PM EDT

After more than 12,000 years, the girl scientists call Naia has returned from the underworld. Her bones, long preserved in their watery tomb in Mexicos Yucatan peninsula, offer a direct link to a mysterious past. And now her DNA is helping to answer one of the most enduring questions in prehistory: Who were the first people to populate the new world?

The newly emerging answer amounts to a convergence of theories. It suggests people reached North America earlier that once thought, and that those same people are also the ancestors of living native Americans.

This is a bonanza find, said Eduard Reinhardt, a micropaleontologist at McMaster University in Hamilton, Ontario. The quality of the data that were getting is exceptional.

An experienced diver, Dr. Reinhardt is one of the scientists directly involved in examining the site where the Naia skeleton was first discovered in 2007. After many millennia, the change in sea level since the end of the last ice age has put the floor of the vast chamber under 40 metres of water. Researchers in scuba gear must swim through the passage where Naia took her final steps, and glide over the precipice where she plunged to her death into what has been named Hoyo Negro, or black hole.

The bottom drops out as you get into that big cavern, Dr. Reinhardt said. Its like a cathedral. Your light just dances off the walls.

The scientific payoff has been equally impressive.

Naias skull is intact and well preserved, which reveals what she looked like when she was alive. At the same time she has yielded her mitochondrial DNA a form of DNA that is inherited only along the maternal line which scientists successfully extracted from one of her teeth.

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Grim discovery sheds new light on when humans came to the Americas