One day in early July, when Thomas Urban was driving to Hill Air Force Base in the Utah desert, looking through the glass window, he suddenly noticed some strange footprints on the ground.
At first, Thomas didn’t notice them either. “Looking from the window of a moving car, I don’t even think it’s a human footprint“, said archaeologist from Cornell University who is working on a project in cooperation with the US Air Force.
But when Daron Duke, a colleague of Thomas’s who was traveling with the suggested bus, they stopped to get off and take a closer look. The two archaeologists were surprised to see that it was indeed the alternating and evenly spaced footprints as if someone had walked on the trail going forward.
There are footprints that belong to adults and there are footprints as small as a 5-year-old child. But the strangest thing that Thomas and Duke noticed about these footprints was this: They seemed to pop up and down.
On certain days, these footprints will appear on the ground. But on another random day, when the archaeologists returned, they disappeared into the desert of nothingness.
In this Utah Field and Test Ground, a 1 million-acre area demarcated by the US military, it is impossible for civilians to walk barefoot in the sand, Thomas said.
So where did these ghostly footprints come from? he wondered.
Back at Hill Air Force Base, Thomas and Duke retrieved a ground-penetrating radar (GPR). It’s a device that works by shooting radio waves down to the surface of the earth and capturing the reflected waves to reveal what’s hidden inside.
Two archaeologists scanned the entire area and found 88 footprints in all. They certainly do not belong to modern people. Based on the structure that Thomas scanned, he determined that these must be human footprints walking on shallow water.
Every time they lift their feet, the sand will immediately fill in part of the rut left behind. It’s like you’re walking on the beach, but underneath the sand is a layer of mud to keep some of the footprints imprinted down after thousands of years.
If Thomas’ argument is correct, the footprints in the Utah desert must be at least 10,000 years old, when the area was still flooded. Even he thought they must be dated even further.
That’s because a mile away from where they were discovered, archaeologists have discovered a hunter-gatherer camp dating back 12,000 years. This could be exactly where these people are headed.
At the hunting camp there is an ancient fireplace, stone tools for cooking and a pile of more than 2,000 animal skeletons. There, archaeologists also found burnt tobacco seeds, the earliest evidence of human smoking.
“The most likely explanation is that they appeared 12,000 years ago, during the last phase of the last ice age Pleistocene (lasted from 2.6 million to 11,700 years ago).“, said Thomas.
If so, this would be one of the earliest surviving footprints on the North American continent. “We clearly found something more valuable than we expected“, said Anya Kitterman, the officer overseeing the archeology at Hill Air Force Base.
“A discovery that you only come across once in your life.”
Returning to the strange disappearance of the footprints, the next question is when do they appear and when do not?
Thomas and scientists tracked and found that ghost footprints in Utah will often appear after rainy days. At that time, water and moisture will make them darker and stand out more than the surrounding soil.
On the contrary, on sunny days, the water evaporates will make the foot prints dry. And surprisingly, they will be filled with salt so that the rut doesn’t even appear anymore. The whole area returned to a flat landscape.
To explain this, we have to go back to 10,000 years ago when the area was a salt lake, similar to the nearby Great Salt Lake which is now considered the largest saltwater lake in the Western Hemisphere.
These ancient salt lakes were dried up by climate change during the last ice age. The hot sun evaporates the water, leaving behind a large amount of salt that once floated above.
And the people, the prehistoric Americans, didn’t wait for the water to evaporate. As soon as the Utah desert became a shallow water, they came here and left footprints.
The former Utah desert was also a huge saltwater lake.
When the wetlands were completely dry, salt eventually filled their footprints and preserved them to this day. On sunny days, the salt hides the ancient footprints in a perfect veil as the water is absorbed deep into the surrounding sediments, synchronizing the colors of the entire landscape in the area.
But on rainy days, the water will dissolve the salt and the mud underneath will be exposed, creating a darker, wetter patch of sediment. The rains also drag the timeline back 12,000 years over an old landscape. It would reveal the footprints of the ancients, as if their silhouettes had just passed here.
Working on a project in partnership with the US Air Force, Thomas Urban was one of the pioneer archaeologists who developed the ground-penetrating radar (GPR) survey technique. This technique allows him to redraw the footprints in the sediment, which in turn can recreate the lives of prehistoric souls.
For example, when analyzing pressure on a sediment surface, archaeologists can guess the weight, body size and age of the person who walked on it. The distance between the footprints also revealed the speed at which they were moving, the movements they might be making.
Last September, at an archaeological site in the salt desert in New Mexico, scientists found 60 “ghost footprints” belonging to a group of prehistoric people who lived 23,000 years ago.
A trail of megafauna shows these prehistoric people chasing a giant sloth. They trampled on its tracks, accelerating at its speed. There was a deep footprint that showed someone had crossed a puddle while holding a child in their arms.
The person then puts the child down at one point. Its footprints first imprinted on the ground. But then the baby is picked up again and the two rush to an unknown point, where the footprints disappear.
By this time, the group may have reached the edge of the lagoon. The sloth was now surrounded by prehistoric people. It stood up on its hind legs, spinning and seemingly trying to defend itself. The children seemed scared and they ran back to the lagoon, letting the adults continue to surround the sloth.
That’s what ground-penetrating radar technology can reveal from the footprints, while, at all, not destroying the specimen. Thomas now wonders if, in addition to Utah and New Mexico, these footprints appear elsewhere in the United States?
Along with his GPR devices and the coordination of the US Air Force, he continues to travel on a journey to find ghost footprints, to recreate the lives of the souls that walk on them. .
“Seeing footprints is seeing human presence. And these footprints allow us to look back to a distant past, very different from what we see today.“, said Thomas.
“The western United States seems to have many similar areas that may contain prehistoric human footprints. We’ve found two now, and we’ll probably find more of them in the future.”
Tham khảo Sciencealert , Smithsonianmag , Nytimes , Nature , Vice , Nationalgeographic