It is known that human beings have been migrating to other regions of the world over time. But perhaps the timing of this may not really be what you imagined.
One of the places in the world that functions as a time capsule like no other is the Coxcatlan cave in Mexico’s Tehuacan Valley. That’s because the cave floor is a history book, detailing thousands of years of food and technology from the planet’s ancient inhabitants.
And finally archaeologists from the United States and Mexico have excavated the first chapter of this history book. They used advanced dating techniques to be able to determine the age of the bones of animals that were buried among the oldest layers of the cave.
With that, they had amazing results. They suggested that humans had been present in the region for 33,000 years. That’s thousands of years before the ice sheets peaked, about 20,000 years ago, which is how long current evidence suggests humans were in the Americas.
For researchers to rethink their theories will still need some radiocarbon measurements. However, the results of this recent study, which was led by archaeologist Andrew Somerville of Iowa State University, should set a fire to the debate over the timeline of human migration to the center of the Americas.
“We were surprised to find these really ancient dates deep in the cave, and that means we need to take a closer look at the recovered artifacts from these levels,” said Somerville.
The discovery makes it clear why the Tehuacan-Cuicatlan Valley in southern Mexico is a UNESCO World Heritage Site. In addition to hosting great biodiversity, its dry climate has preserved records of human presence for thousands of years. This made the location very valuable to researchers interested in the spread of humans throughout the New World.
And in this archaeological treasure, the Coxcatlan cave is a real gem because of its deep layers of sediment and dry conditions that give researchers a chronology of activity dating back at least 11,000 years.
It was from the mid-1990s that scholars and academics began to have doubts about how this cave “book” should be read. They began to have concerns about dating some botanical species and saying the pages might be out of order.
This might not be just one or two layers, but about three-quarters of the plant materials that were excavated from the cave. As much as new research has since been defending the cave’s timeline, its reliability has been somewhat shaken.
The lower layers of the site have not yet been fully analyzed. And Somerville and his team realized that work needed to be done to clarify the cave’s chronology.
“We weren’t trying to think through this debate or even find really old samples. We were just trying to put our agricultural study on a tighter schedule,” said Somerville.
They performed radiocarbon dating by mass spectrometry on 14 bones of animals such as hares, rabbits and deer, which had been excavated from the cave. With that, they created a catalog of dates describing when the animals lived.
Several of the rabbit bones and femur of a hare have been dated to approximately 33,000 years. This era not only preceded all records currently held, but it would also be isolated from the rest of the world by climate change.
“Pushing the arrival of humans to North America more than 30,000 years ago would mean that humans were already in North America before the period of the Last Glacial Maximum, when the Ice Age was at its worst. Large parts of North America would have been inhospitable to human populations. The glaciers would have completely blocked any overland passage from Alaska and Canada, meaning that people would likely have had to come to the Americas by boat from the Pacific coast,” concluded Somerville.