How long have humans been in the Americas? If you said 13,000 years, move to the back of the line with the rest of those espousing that conventional wisdom. A new discovery in a cave in Mexico may be proof that it was occupied by humans 20,000 years before that – putting the history of the western continents very close to a “this changes everything” moment. Who were these earliest settlers and where did they come from?
“We weren’t trying to find these really old dates at all. 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.”
Andrew Somerville, an Iowa State University archaeologist and lead author of a new paper on the discovery published in the journal Latin American Antiquity, told Popular Science that his team was studying the history of agriculture in the area around Coxcatlan Cave in the Tehuacan Valley of southern Puebla, Mexico. That cave is a key source because its dryness has preserved layers of dust, rocks, charcoal, and decaying plants that help peel away the layers of that history. It’s been studied before, but the results have been contradictory, so Somerville and his team brought a new carbon dating technique to analyze animal bones in the layers and get a more accurate lock on their age.
Those bones – mostly from deer and rabbits – were found throughout the layers so they came from different times and climate conditions. And the area was known to have been farmed by humans who arrived the conventional way – across the now-gone land link from Siberia to the Pacific Northwest. That still didn’t prepare the team for the shock that the earliest ones were 33,000 years old. What if they weren’t from animals trapped deep in the cave – what if they had been brought there by humans?
“Determining whether the stone artifacts were products of human manufacture or if they were just naturally chipped stones would be one way to get to the bottom of this. If we can find strong evidence that humans did in fact make and use these tools, that’s another way we can move forward.”
Let’s assume some bones contain the telltale signs of human toolmaking and usage. Who made them 33,000 years ago, long before the period of the Last Glacial Maximum, when the Ice Age made large parts of North America uninhabitable? That would mean these Coxcatlan Cave residents arrived by boats sailing down the Pacific coast. Cut marks on the bones or signs of cooking might help identify them, but the bones are still in the cave and Somerville is in Iowa due to the pandemic. While he can’t wait to get back and look for a “smoking gun” or gnawed thigh bone, he’s hesitant to make any predictions.
“This is such a contentious issue, and it is something that’s been debated for so long that I really hesitate to come down strongly on one side or the other. Originally, I had no clue they were this old, so I wasn’t paying that close attention. But, I will say that my impression of it, and the impression of the original analysts of these animal bones is that, yes, they do appear to have been modified by humans.”
We’ll just have to wait and see. In the meantime, stay at the back of the line until you learn it’s not always wise to trust conventional wisdom.