Dating of the oldest human footprints in North America could yield clues to Mexico's climate 7,000 years ago, researchers from a British university say. Two sets of footprints found in the Chihuahuan desert in northeastern Mexico are the oldest evidence of humans in the area, scientist at the University of Liverpool said. The prints were preserved in sediments known as travertine -- a mineral that precipitates out when water percolates through limestone rocks -- suggesting the area must have been far wetter than it is today, they reported in the Journal of Archaeological Science. "It's in the middle of the Chihuahua desert, everyone always thinks that deserts are hot, arid and hostile but these footprints show us that during the Holocene, the desert was just coming out of a period of glaciation and had only just started to dry out," researcher Nick Felstead says. "It's a window into a time when the desert was wet enough to support a much greater range of life." The study has been published in the Journal of Archaeological Science.