In this June 2013 photo provided by National Geographic, diver Susan Bird, working at the bottom of Hoyo Negro, a large dome-shaped underwater cave in Mexico's Yucatan Peninsula, brushes a human skull found at the site while her team members take detailed photographs. Thousands of years ago, a teenage girl fell into this deep hole and died. Now, her skeleton and her DNA are helping scientists study the origins of the first Americans. An analysis of her remains was released Thursday, May 15, 2014 by the journal Science. Her DNA links her to an ancient land bridge connecting Asia and North America, and suggests she shares ancestors with the modern native peoples of the Americas.