Surprisingly old stone points found in a Mexican cave are the latest intriguing discovery among many to raise questions about when humans really arrived in the Americas.
For most of the 20th century archaeologists generally agreed that humans who had crossed the Beringia land bridge from Siberia to North America only ventured further into the continent only when retreating ice sheets opened a migration corridor, about 13,000 years ago. But a few decades ago, researchers began discovering sites across the Americas that were older, pushing back the first Americans’ arrival by a few thousand years. Now, the authors of a new study at Mexico’s Chiquihuite cave suggest that human history in the Americas may be twice that long. Put forth by Ciprian Ardelean, an archaeologist at the Autonomous University of Zacatecas (Mexico), and his colleagues, the new paper suggests people were living in central Mexico at least 26,500 years ago.
Chiquihuite cave is perched high in the Astillero Mountains, 9000 feet above sea level and 3,280 feet higher than the valley below. Excavations there were launched when a 2012 test pit unearthed a few stone artifacts that suggested a human presence dating back to the Last Glacial Maximum between 18,000 and 26,000 years ago. More extensive excavations detailed in the new study were carried out in 2016 and 2017, unearthing some 1,900 stone points or possible tools used for cutting, chopping, scraping, or as weapons.
The artifacts were dated by 46 different radiocarbon samples of adjacent animal bones, charcoal, and sediment samples. To the team, they represent a previously unknown technological tradition of advanced flaking skills. More than 90 percent of the artifacts were of greenish or blackish stone, though those colors are less common locally, suggesting to the authors that they were singled out as desirable. The bulk of the material is from deposits dating to between 13,000 and 16,600 years ago, leading the scientists to hypothesize that the humans may have used the cave for more than 10,000 years.
Davis also laments a lack of evidence for domestic life in the cave. “We usually see things like butchering animals and making food,” he says. “They did find lots of animal bones but they say there is no evidence of butchering and that’s really strange. There’s also an absence of things like fire pits, or pits in the ground for storing things, or unusual distributions of objects.”
Ardelean believes some of those features might lie tantalizingly close by, yet be difficult or impossible to uncover. The current excavation is taking place far inside the large cave. “Most activities like cooking and eating happened right at the entrance,” he says. “And that entrance isn’t accessible, it’s buried under tons of debris that has fallen from the top of the mountain.”
When the oldest pre-Clovis sites are plugged in, the model suggests that humans populated the Americas before and during the Last Glacial Maximum some 19,000 to 26,500 years ago. That would mean that humans not only arrived in the Americas earlier than is commonly believed, but that they somehow circumvented the era’s massive ice sheets.
If the Americas begin to look more heavily populated by distinct groups of people after these dates, Ardelean believes the earlier pre-Clovis sites, each with distinct types of technologies or artifacts, tell a different tale.
A theory that these peoples migrated by travelling down the Pacific coastline 14,000 to 15,000, or even as long as 20,000 years ago, has been steadily gaining support as excavations turn over more evidence, though uncovering their tracks is complicated due to past changes in sea levels. Another possibility is simply that people entered the Americas by land before the glaciers blocked the route into the continent’s interior. The model also suggests that a second, more widespread peopling of the Americas unfolded during a period of sudden and dramatic warming about 12,900 to 14,700 years ago. Becerra-Valdivia says this is evidenced by a spike in archaeological sites and the emergence of stone tool traditions like Clovis. Genetic research, she adds, also “points to marked population growth between around 15 to 16 thousand years ago.”
“I think that the human presence during the Last Glacial Maximum was extremely diverse, and there were multiple arrivals from multiple directions,” he says. “I believe humans were culturally diverse and potentially genetically diverse. There was no such thing as a single arrival.”
https://www.smithsonianmag.com/science-nature/when-did-humans-reach-america-mexican-mountain-cave-artifacts-raise-new-questions-180975385/