Radiocarbon dating measures the age of organic materials based on their content of the radioactive isotope carbon 14.
According to archaeologist David Anderson of the University of Tennessee, however, minerals in seawater can sometimes alter the carbon 14 content of bones, resulting in inaccurate radiocarbon dating results.
The remains were found some 50 feet (15 meters) below sea level in the caves off Tulum. But at the time Eve of Naharon is believed to have lived there, sea levels were 200 feet (60 meters) lower, and the Yucatán Peninsula was a wide, dry prairie.
The polar ice caps melted dramatically 8,000 to 9,000 years ago, causing sea levels to rise hundreds of feet and submerging the burial grounds of the skeletons. Stalactites and stalagmites then grew around the remains, preventing them from being washed out to sea.
González has also found remains of elephants, giant sloths, and other ancient fauna in the caves.
(Learn more about how caves form.)
Human Migration Theories
If González's finds do stand up to scientific scrutiny, they will raise many interesting new questions about how the Americas were first peopled.
Many researchers once believed humans entered the New World from Asia as a single group crossing over the Bering Land Bridge no earlier than 13,500 years ago. But that theory is lately being debunked.
Remains found in Monte Verde, Chile, in 1997, for example, point to the presence of people in the Americas at least 12,500 years ago, long before migration would have been possible through the ice-covered Arctic reaches of North America.
(Related: "Clovis People Not First Americans, Study Shows" [February 23, 2007].)
Confirmation of Eve of Naharon's age could further revolutionize the thinking about the settlement of the Americas.
This September, González will begin excavating the fourth skeleton, known as Chan hol, which he says could be even older than Eve.
The Chan hol remains include more than ten teeth, which will allow researchers to date the specimen and gather information about Chan hol's diet.
"When we learn more about the [Mexican finds] we'll be able to better evaluate them," said Carlos Lorenzo, a researcher at the Universitat Rovira i Virgili in Tarragona, Spain, an expert on the subject who was not involved in the current study.
"But in any case, if it's confirmed that Eva de Naharon is 13,000 years old, it will be a fantastic and extraordinary finding for understanding the first settlers of America."
González said he and his team hope to publish the full results of their analysis after the excavation of the fourth skeleton.
"We're not yet in the phase of research of determining how they arrived," he said. "But when we have more evidence we may be able to determine that."
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