When you visit White Sands National Monument in New Mexico, you will witness endless waves of bright gypsum. It's beautiful, but a team of researchers led by scientists at Cornell University was more interested in what was hiding under the sand.
The team used ground-penetrating radar, which has been used to discover more stones near Stonehenge, to investigate the movements of mammoths, humans and giant sloths from 12,000 years ago. These tracks are normally difficult to see unless conditions are perfect. The researchers refer to them as "ghost tracks."
The scientists published a paper, "3-D radar imaging unlocks the untapped behavioral and biomechanical archive of Pleistocene ghost tracks," in the journal Scientific Reports on Monday.
"We never thought to look under footprints," said lead author Thomas Urban in a Cornell release. "But it turns out that the sediment itself has a memory that records the effects of the animal's weight and momentum in a beautiful way. It gives us a way to understand the biomechanics of extinct fauna that we never had before."
The radar revealed a fascinating scene from the past consisting of a double trackway of human footprints stretching over 2,600 feet (800 meters). It showed the movements of what was likely a single person walking one way and then returning on roughly the same path. Mammoth tracks cross over the human tracks.
One of the mammoth tracks is special. It shows where a human stepped into the track later, leaving a telltale footprint behind. This gives researchers a rare glimpse into how humans and mega-fauna may have interacted all those years ago.
This study shows how ground-penetrating radar can reveal previously hidden secrets from the past, even ones as subtle as footprints. "The technique could possibly be applied to many other fossilized footprint sites around the world, potentially including those of dinosaurs," said Urban.