Around 12,000 years ago, a short teenage girl was wandering a system of caves, likely searching out water, when she fell into a deep pit and cracked her pelvis. She likely died almost instantly, and her body remained there untouched until researchers discovered it in 2007, submerged under water that had filled the cave when glaciers began melting 2,000 or so years after her death. Those researchers have been studying her remains in the years since, and now her skeleton is helping to settle a big debate: the question of where the earliest Americans actually came from.

"This is one step toward resolving that question." The going theory is that the first Americans, known as Paleoamericans, came from Beringia — a northern area that includes the land bridge once connecting Russia and Alaska. But skeletons found throughout the Americas have posed a problem: these early Americans don't resemble modern Native Americans, nor the Siberians from which they're believed to have descended. That's left open the possibility that a second migration of humans from some other region also populated the Americas. "Were they separate immigrations," asks research leader James Chatters, "or was evolution the issue?"

This new skeleton, said to be one of the six oldest ever found in the Americas, serves as some of the best evidence yet toward confirming the latter: that the first Americans did in fact come from Beringia and later evolved features distinct from modern Native Americans. "This expedition produced some of the most compelling evidence to date of a link between Paleoamericans … and modern Native Americans," Chatters says in a statement.

Grid View Image courtesy of Paul Nicklen/National Geographic

Image courtesy of Paul Nicklen/National Geographic

Photo by Daniel Riordan Araujo

Photo by Daniel Riordan Araujo

Photo by Daniel Riordan Araujo

Photo by Daniel Riordan Araujo

Image courtesy of Paul Nicklen/National Geographic

Photo by Daniel Riordan Araujo

That's because the skeleton, which the researchers have named Naia, has features distinct from modern Native Americans but can also be linked to them through DNA — something that hasn't been possible with earlier remains. Naia was also found in the south of Mexico, in the Yucatán Peninsula, which is far lower in the Americas than similar skeletons found so far, furthering the evidence that Paleoamericans hailed from a single origin and continued to travel.

"We had no idea what we might find when we initially entered the cave." This isn't a smoking gun for that theory, but it furthers its case. "This is one step toward resolving that question," Chatters says. "This is only one step and only one individual." The researchers' findings are begin published today in the journal Science.

Though Chatters is quick to hedge those results based on this work's sample size of just a single skeleton, it's still a big step toward answering a question that he's been looking into for nearly two decades. He was one of the leaders behind the 1996 discovery of and research on Kennewick Man — a skeleton over 7,000 years old that was found in Washington state and posed these same questions of ancestry. "For the nearly 20 years since Kennewick Man turned up," he says, "I've been trying to understand why they look so different."

His break came in 2007, when a group of divers discovered the pit that Naia fell into, known as Hoyo Negro ("black hole" in English), and found her skull near the bottom of the 100-foot-deep, bell-shaped cavern. "We had no idea what we might find when we initially entered the cave, which is the allure of cave diving," Alberto Nava, part of the Bay Area Underwater Explorers team that first found Naia, says in a statement. To access the cave, the divers had to climb down a 30-foot ladder and then swim through 200 feet of tunnel before coming to the pit.

Before Hoyo Negro was underwater, it was more than just Naia that fell into it. Many animals fell in too, and researchers found in the pit the bones of sabertooth tigers, pumas, coyotes, and sloths, among other animals. Naia is believed to have been 15 or 16 years old when she fell in, and researchers say that may have happened anywhere between 12,000 and 13,000 years ago. Most of the skeleton still remains in the cave today, but due to unauthorized divers coming in and tampering with various remains, the researchers felt it necessary to remove Naia's skull along with four other pieces just this March.