America is the last continent that man settled. But when the first Native American ancestors arrived there is highly controversial. Now archaeological finds in a cave in Mexico are fueling the debate. Researchers have discovered hundreds of stone blades, animal bones and plant remains that are more than 30,000 years old. This suggests that people were present in this region more than 10,000 years earlier than previously thought. They must have immigrated to America before the peak of the last ice age. The stone tools also have a design that none else has ever documented.
The first people to set foot on the American continent came from Asia, DNA comparisons show. These first immigrants probably crossed the Bering Strait to the new continent. During the last ice age, a 1600-kilometre-wide and almost 5000-kilometre-long land bridge connected Asia and North America. But when this first settlement of the New World took place is still puzzling – and hotly debated. For a long time, the hunters of the Clovis culture, who left traces in many places in North America some 13,000 years ago, were considered the origin of all the indigenous peoples of this continent.
According to this theory, their immigration only became possible when an ice-free corridor opened between the eastern Laurentide ice sheet and the Cordillera Ice Sheet in western North America.
Find in a mountain cave in Mexico
But since then, archaeologists have discovered traces of human presence in many places in North and South America, some of which are several thousand years older than the Clovis culture. These include a 14,500-year-old mammoth battlefield in Florida, but also relics of up to 18,000 years old from the southern tip of South America.
Given the enormous distance of these settlements from the likely arrival of the first “Native Americans”, this has long cast doubt on the Clovis hunters as the first arrivals – and also on the timing of their arrival. According to this, the first humans must have come to America much earlier, possibly even at the height of the last ice age or shortly thereafter. Because the path through the ice-free corridor was still closed at that time, these first arrivals must have migrated south along the Pacific coast instead. Despite the finds of pre-Clovis relics, this theory of earlier arrival remained controversial.
Now, a discovery in the highlands of Mexico provides new evidence of a far earlier human settlement of America. Ciprian Ardelean of the Autonomous University of Zacatecas and his colleagues made the discovery during excavations of the Chiquihuite Cave, 2,740 meters above sea level, on the mountainside.
There, archaeologists had already discovered the first evidence of an early presence of humans during a test excavation in 2012. In 2016 and 2017, they therefore carried out a comprehensive excavation. In several layers of the cave floor, the researchers came across animal bones and plant remains as well as man-made stone tools.
To determine the age of these finds, the researchers performed radiocarbon dating for 59 samples and additionally dated samples of rock from the found layers using optically stimulated luminescence.
More than 30,000 years old
The dates revealed that the oldest finds in this cave could be more than 30,000 years old. “According to our results, the start of the discovery layer C is 33,150 to 31,400 years – and thus before the last glacial maximum,” Ardelean and his team report. According to this, people must have been present in America even before the peak of the last ice age and have made their way to Mexico.
Who these people were, however, remains open. Scientists have failed to isolate the DNA of the former cave dwellers. The design of the stone tools, however, suggests that it may have been a culture of its own, as yet unknown. Because they are very different from those previously known from America, as the archaeologists explain.
The stone tools include differently shaped blades, tips and wedges, which have been made in some complex ways. In addition, the majority of these tools do not consist of the coarse, grey limestone lying everywhere, but of greenish and blackish-colored, particularly dense and even variants of this rock. These occurred only sporadically in the vicinity of the cave and must therefore have been specifically searched. “The systematic geological selectivity that emerges in the production of these tools speaks to a conscious choice and a deep knowledge of the available stone raw materials,” Ardelean and his colleagues say. Combined with the special design, this collection of finds represents a stone culture that is not the same as any of the previously known from America.
According to the researchers, their findings provide further evidence of the early presence of humans on this continent and at the same time illustrate the cultural diversity that prevailed in the early days. Ruth Gruhn of the University of Alberta sees it similarly. In an accompanying commentary, she writes: “This Mexican site is now joined by about half a dozen other documented archaeological sites that suggest evidence of human settlement 30,000 to 20,000 years ago.” Thus it is clear that the theory of Clovis culture as the starting point of all early cultures of this continent is outdated. “It is clear that people were present in North America long before clovis technology was developed,” Gruhn said. But who these people were, when and where they set foot on the continent and how they moved on from there, is still puzzling.