Excavated tools in a Mexican cave show that modern humans walked the American continent roughly 30,000 years ago, roughly twice as early as thought. This is evident from two new scientific studies published on Wednesday in the leading scientific journal Nature .

Until now, the scientific consensus was that people first reached North America from East Asia about 15,000 years ago. They did this by crossing a dry land bridge between Siberia and Alaska.

The researchers write in Nature that they dug up nearly two thousand limestone tools in the Chiquihuite Cave, located in a mountainous region of northern Mexico. The objects may have been used as blades and spearheads.

According to archaeologist and principal investigator Ciprian Ardelean at the Autonomous University of Zacatecas in Mexico, the oldest artifacts are between 26,000 and 18,000 years old, at the peak of the last Ice Age.

Other scientists are still skeptical

The possible fact that humans populated North America much earlier is greeted with caution by other scientists, who reviewed the findings in Nature .

For example, they wonder whether the objects, which are very accurately dated, are actually man-made or possibly formed by natural processes. The researchers in Mexico will have to come up with more evidence for this.

Homo Sapiens, or modern man, appeared on the scene in Africa about 300,000 years ago and then spread to the rest of the world.