Here’s what you’ll learn when you read this story:

• Fossilized footprints in Saudi Arabia show human traffic on the cusp of a subsequent ice age.
• Like carbon dating, scientists use isotopes and context clues to calculate the approximate age of fossils.
• These human prints were surrounded by animals but not hunted animals, indicating humans were just thirsty.

A uniquely preserved prehistoric mudhole could hold the oldest-ever human footprints on the Arabian Peninsula, scientists say. The seven footprints, found amidst a clutter of hundreds of prehistoric animal prints, are estimated to be 115,000 years old.

Many fossil and artifact windfalls have come from situations like this special lakebed in northern Saudi Arabia. Archaeologists uncovered the site, deep in the Nefud Desert at a location nicknamed “the trace” in Arabic, in 2017, after time and weather wiped the overlying sediment away. It’s easy to imagine that a muddy lakebed was a high-traffic area in the Arabian Peninsula over 100,000 years ago.

When populations move on, these prints are left behind until they’re covered over. In the far, far older Burgess Shale event, some of the oldest organisms ever found were preserved intact because they likely fell into a mudslide and were killed instantly. An entire armored nodosaur was found in unprecedentedly good shape because it was encased in mud and in the cold of the ocean floor. If there were a finder’s fee for incredible archaeology, a lot of it would be paid to mud.

In their paper, the scientists actually examine why that ancient mud was so special at all:

“An experimental study of modern human footprints in mud flats found that fine details were lost within 2 days and prints were rendered unrecognizable within four, and similar observations have been made for other non-hominin mammal tracks.”

That means their special, tiny batch of preserved footprints were made in unique conditions that also form a kind of “fingerprint” for pinning them all to the same timeframe. From there, scientists started to look at who made the footprints. Homo sapiens weren’t the only upright humanoid primate in the game, but the evidence, the scientists say, suggests we were the ones traipsing through the drying lakebed:

“Seven hominin footprints were confidently identified, and given the fossil and archeological evidence for the spread of H. sapiens into the Levant and Arabia during [the era 130,000 to 80,000 years ago] and absence of Homo neanderthalensis from the Levant at that time, we argue that H. sapiens was responsible for the tracks at Alathar. In addition, the size of the Alathar footprints is more consistent with those of early H. sapiens than H. neanderthalensis.”

The lake that forms Alathar today was likely part of a prehistoric highway that drew all the large animals in the area, forming a corridor dotted by freshwater rest areas that living things could travel on as they migrated with the weather or the changing climate. In this case, scientists found very little of the other factors that accompany prehistoric human travel, like knife or tool marks on animal bones indicating hunting.

“The lack of archaeological evidence suggests that the Alathar lake was only briefly visited by people,” the scientists conclude. “These findings indicate that transient lakeshore use by humans during a dry period of the last interglacial was likely primarily tied to the need for potable water.”

These Homo sapiens could be the last ones on their way through a temperate place as an impending ice age descends. That would also explain why their tracks weren’t tracked over by another group, at least not before an entire fresh layer of sediment accumulated.