At least one part of the Americas was already occupied by humans before that time, however, says new research on the skeleton of a male youth found in Chan Hol cave near Tulúm, Mexico. Dubbed the Young Man of Chan Hol, the remains date to 13,000 years ago, according to a paper published in the journal PLOS ONE.

How he arrived at the location remains a great mystery given the timing and the fact that Mexico is well over 4,000 miles away from the Bering land crossing.

“Scenarios of travel by boat along the Pacific shoreline, the ‘Kelp Highway,’ must be taken seriously, but alternative migration routes by boat from Europe along the Greenland ice margin or via Antarctica are also possible, though highly speculative,” lead author Wolfgang Stinnesbeck of the Institute of Geosciences at Heidelberg University said.

“If travel by boat is correct,” he added, “then likely camp sites are now set underwater due to the early Holocene rise of sea level.”

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Chan Hol, meaning “little hole” in a Mayan language, is also underwater now, and was first explored by diver Kim Davidsson in 2004. It has since become a popular site for cave diving in Mexico.

Scientists grew interested in the caves as well, with exploratory dives beginning around 2006. That same year, co-author Arturo González of the Desert Museum in Saltillo, Mexico and his team discovered the remains of Young Man of Chan Hol. Additional human remains have been found in underwater caves near Tulúm, which is 80 miles south of the beach resort city of Cancún.

For the new study, González, Stinnesbeck, and their colleagues dated the Young Man of Chan Hol’s remains by analyzing the bones’ uranium, carbon, and oxygen isotopes, which were also found in stalagmite that had grown through the pelvic bone.

The scientists believe that the resulting age of 13,000 years could apply to at least two other skeletons found in caves around Tulúm: a teenage female named Naia and a 25–30-year-old female named Eve of Naharon.

González said that the shape of the skulls suggests that Eve and the others “have more of an affinity with people from Southeast Asia.” He and his team further speculated that the individuals could have originated in Indonesia.

During the lifetime of the Young Man of Chan Hol, the sea level of the area was much lower than it is now. As a result, the researchers think that the cave system near Tulúm would have been dry and accessible from at least 100 feet below present levels.

“In consequence, the entire area must have been considerably drier than today,” Stinnesbeck said. “Instead of a coverage by jungle, there must have been dry savannas, and surface water was absent.”

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The cave system would have offered cool shelter and even probable water sources during this time. Still, given that there must have been a shortage of fresh water at ground level, the region would seem to have been an unlikely choice for an early human settlement.

Recently, Stinnesbeck and his team analyzed isotopes present in the teeth that belonged to some of the individuals found within the caves. They also looked at similar isotopic signatures for fossil animals found in the area. Intriguingly, the isotope composition of the human teeth proved to be a better match for wildlife that lived in the interior of the Yucatán Peninsula.