The Coxcatlan Cave in Mexico’s Valley of Tehuacan has housed tens of thousands of years of human history through the millennia. Records of the early domestication of maize and the start of agriculture have been preserved in layers of dust, rocks, charcoal, and decaying plants. But under them, all lies something even more surprising: what might be one of America’s earliest human recordings.
Animal bones discovered in the lowest stratum, according to recent radiocarbon analysis, are between 28,000 and 31,000 years old. The most widely accepted idea currently is that people originally arrived in the Americas some 14,000 years ago, trekking through a now-submerged continent that linked Alaska and Siberia.
If the discoveries are confirmed by future research, they will assist to redefine North America’s human past.
Andrew Somerville, the study’s main author, adds, “We weren’t intending to locate these incredibly old dates at all.” Instead, the crew was looking into the region’s agricultural past. They utilized a newer methodology on animal bones recovered at different strata in the cave after prior carbon dating techniques yielded inconsistent findings. “We just realized that none of these lower levels had ever been dated. We anticipated them to be comparable to what the first excavator predicted 12,000 years ago. As a result, we were taken aback. We were anticipating them to be approximately 20,000 years old, but they were around 20,000 years older.”
Because the cave had been dug 60 years before, the evidence had been stashed in plain sight in crates at a research center for decades. Somerville adds, “I believe this simply goes to illustrate how crucial it is to finance archaeological preservation and keep all these ancient collections.”
The bones date from before the land bridge was built and originate from prehistoric horses, gopher tortoises, and pronghorn antelope. And the species speak for themselves. They live in an open desert, the sort that can today be found in southern New Mexico and Texas, but not in the area surrounding Coxcatlan. Other discoveries, on the other hand, show that the area would have been more desert-like 28,000 years ago when glaciers moved south. The fact that subsequent strata predominantly include deer bones indicates that the bones are from different climatic periods.
Richard MacNeish, the archaeologist who initially discovered the Coxcatlan Cave, believed that the deepest stratum, which also included what looked to be early stone tools, suggested traces of human occupancy. But, because it would upend a whole paradigm, that categorization has to be reassessed with skepticism.
According to Shane Miller, a Mississippi State University archaeologist who studies early human migrations, showing human residence needs at least two things: a dateable site and “evidence that you have a real human item.”
Somerville claims that these techniques aren’t diagnostic. “There are no lovely triangular projectile tips to be found. These are relatively basic blades or scraper-type tools, and a skeptic would claim that these were chipped stones that formed naturally.” Because of the epidemic, Somerville hasn’t been able to return to the relics, but he hopes to study the tools to ensure that they aren’t, for instance, fragments of the cave roof that broke in the proper manner.
Examining the bones themselves “to search for cut marks, butchering, and traces of cooking” will provide the greatest proof, according to Somerville.
“That’s more like a smoking gun,” says the narrator. “Boom, 30,000 years ago, on a bone, with human-made slash marks.”
Another theory is that the bones were in the cave long before humans arrived—perhaps another predator had settled in 30,000 years ago—and people just built their houses on top.
Another enigma at the site is the 14,500-year gap between the oldest layer and the next most recent, which is between 13,500 and 10,000 years old. Humans abandoned the cave if the earliest deposits were left by them.
Somerville believes it’s not out of the question. The “Last Glacial Maximum,” when the Tehuacan region was apparently at its most hostile, correlates to the hole in the archaeological record. One theory for the gap is that the cave’s residents “migrated out of the valley, and then people didn’t come back and repopulate the valley for [14,500] years, at which point the climate began to ease up,” but he warns that this is simply speculation.
Even though the bones are more than ten thousand years older than the commonly recognized timeframe for human habitation, they are found with a succession of other recent discoveries that point to a far earlier past. Last year, a study published in Nature revealed a likely stockpile of 19,000-26,000-year-old stone tools in northern Mexico, which it claimed: “pushes back estimates for human spread to the region probably as early as 33,000-31,000 years ago.”
However, such sites also suggest that early people traversed an ice-covered Alaska on their way from Asia to America. “By boat is the most plausible explanation,” Somerville adds. “They’re hopping down the coast, sleeping along the way, erecting camps where they’re gathering marine animals, crabs, and kelp forest resources.”
While there is plenty of archaeological evidence from humans traveling interior Alaska approximately 13,000 years ago, there isn’t much to go on in terms of a possible coastal route. “The great issue back then was that sea levels were lower, so any beachfront camping would be submerged by 100 meters.”
Despite the unsolved concerns, Somerville says he’s inclined to believe the site will turn out to be human. “I hate to come down firmly on one side or the other since this is such a difficult topic that has been fought for so long,” he adds. Even so, he’s worked with bones and potential instruments before. “At first, I had no idea they were so ancient, so I wasn’t paying attention. But I will add that, in my opinion, and in the opinion of the initial analyzers of these animal bones, they do look to have been altered by humans.”