Archaeologists excavating a cave in central Mexico have found ancient stone tools that suggest people may have arrived in the Americas as many as 33,000 years ago -- far earlier than scientists previously believed.
A team led by Ciprian Ardelean, of the Autonomous University of Zacatecas in Mexico, said that a yearslong excavation of Chiquihuite Cave in the Astillero Mountains turned up nearly 2,000 stone tools that have since been carbon dated to between 25,000 and 32,000 years old, according to the scientific journal Nature.
Among the items found were three pieces of limestone that appeared to be shaped into a pointed stone and a pair of cutting flakes, NBC News reported. They were found in the deepest layer of sediment excavated by Ardelean’s team and may be the oldest tools found thus far in the Americas, according to the news network.
Other artifacts found include blades and projectiles, National Geographic reported. Researchers did not find any human DNA in the cave.
The team’s findings, published Wednesday in Nature, sparked controversy among scientists. Kurt Rademaker, of Michigan State University in East Lansing, told Nature that he saw no clear evidence in photos published Wednesday to show the stones found in Chiquihuite Cave were, in fact, tools.
“If an artifact is a stone tool, you see numerous chips removed from the edge,” he told the journal.
Others questioned whether the stones might have shifted into lower layers of the cave over time, making them appear older. Ardelean conceded the point in an interview with Nature, however, he said the 239 oldest tools found were discovered under “an impenetrable layer of mud formed during the height of the last ice age, so they must be at least that old.”
Loren Davis, an archaeologist at Oregon State University, told National Geographic that the controversy was not unexpected.
“Everybody knows that when you step in the ring at this level, you are looking for an international debate, you’re going to get it, and you should have your defense prepared,” she said. “To me, it’s inevitable.”
Scientists agree that humans first came to North America from Asia, although there is wide debate over when they first arrived.
According to Nature, most scientists believe people first came to the Americas around 15,000 or 16,000 years ago based on the current genetic and archaeological evidence. The prevailing theory is that people used a land bridge to cross over the Bering Strait into the Americas.