Over the millenia, the Coxcatlan Cave, in the Valley of Tehuacan, Mexico has been home to tens of thousands of years of human history. Preserved in layers of dust, rocks, charcoal, and decaying plants are records of the early domestication of corn and the birth of agriculture. But beneath them all is something even more surprising: what might end up being one of the oldest records of humans in the Americas.
Based on a new radiocarbon analysis, animal bones found in that deepest layer are between 28,000 and 31,000 years old. Currently, the most popular theory is that humans first arrived in the Americas around 14,000 years ago, walking over a now-drowned continent that connected Alaska and Siberia.
“We weren’t trying to find these really old dates at all,” says Andrew Somerville, the lead author on the research. Instead, the team was investigating the history of agriculture in the region. But previous carbon dating techniques had led to contradictory results, so they used a newer technology on animal bones found at different layers in the cave. “We just noticed that no one had ever dated some of these bottom levels. We kind of expected them to be similar to what the original excavator suggested, which was around 12,000 years ago. So we were very surprised. They were about 20,000 years older than we were expecting.”
The cave had actually been excavated 60 years ago, so the evidence had been hidden in plain sight in boxes at a research center for decades. “I think this just goes to show how important it is to fund archaeological curation and hold on to all these old collections,” Somerville says.