Controversial cave discoveries suggest humans reached Americas much earlier than thought

A massive haul of stone tools discovered in a cave in Mexico is evidence that people occupied the area more than 30,000 years ago. The finding suggests that humans arrived in North America at least 15,000 years earlier than had been thought. The discovery is backed up by a separate statistical analysis incorporating data from sites in North America and Siberia. But some researchers are unconvinced. They question the age of the tools, and whether the artefacts are tools at all, rather than objects created by natural processes.