Scientists have analyzed footprints made thousands of years ago. They were found in White Sands National Park, in New Mexico. The tracks show that humans lived in North America some 5,000 years earlier than past evidence suggested.
The prints were preserved in the mud of an ancient lakeshore. Researchers say they are 21,000 to 23,000 years old. Findings were published last month in the journal Science.
Over time, thousands of footprints have been found in the park. One path shows a woman walking with a toddler. Another shows people hunting a giant sloth.
Researchers measured the carbon in ancient grass seeds to estimate the age of the prints.