When the left and right human footprints (IMAGE ABOVE) were discovered during highway construction in northeastern Mexico in 1961, they were excavated and studied at a local museum. Because their precise location had been lost, researchers searched for the site in 2006 and discovered 11 tracks in the general area – a marshy, spring-fed desert refuge known as Cuatro Ciénegas – where the original prints were believed to have been found. They left the newly discovered tracks in place, but were able to date them to about 7,250 years old based on the decay of minute traces of uranium in the sedimentary travertine in which they formed. But using the same dating technique, geoarchaeologist Nicholas Felstead of Durham University determined that the pair of footprints found in 1961 were about 10,550 years old – 5,000 years older than any others on the continent. This makes these footsteps taken by a Native American in the Chihuahuan Desert the oldest known human footprints in North America.