In 2008, when conservationist Jim Brett came across a set of footprints on a mudflat in Tanzania, he knew he had stumbled upon something valuable.
The footprints turned out to be the best-preserved and largest set of ancient human footprints ever discovered in Africa, covering an area around the size of a tennis court. Mr. Brett immediately notified Cynthia Liutkus-Pierce, a geologist at Appalachian State University.
"The first time we went out there, I remember getting out of the vehicle, and I teared up a little bit," Dr. Liutkus-Pierce told National Geographic. "Human origins is a huge interest of mine: where we came from, and why we are who we are. It was definitely emotional to see our own history in this."
In a study published last month in Paleogeography, Palaeoclimatology, Palaeoecology, Liutkus-Pierce and her colleagues explain that the footprints, which were close to the village of Engare Sero and right by an active volcano known as “mountain of God,” dated to between 5,000 and 19,000 years ago. The footprints belong to prehistoric humans who are anatomically similar to modern humans in the late Pleistocene era.
The researchers analyzed the footprints for clues to how humans lived during an era when climates and temperatures were changing dramatically, much as they are today.
"It'll give us a sense of the group size and structure of these ancient hunter-gatherers," Briana Pobiner, a paleoanthropologist at the National Museum of Natural History and a member of Liutkus-Pierce's team, told The Washington Post. "What's the composition of this group? How many males, how many females and kids, and how many directions are they going? Are they running? Are they walking? Are they walking side by side? … For people who work in prehistory, it's incredibly rare to get that kind of snapshot in time."
The excavation of the Engare Sero tracks was supported by the National Geographic Society’s Committee for Research and Exploration. As reported by National Geographic, geologists on the research team quickly ran into trouble trying to figure out the age of the ash-rich mud that the footprints were imprinted in. They first thought the footprints were the same age as the 120,000-year-old eruption, but later concluded that the ashes had eroded from the nearby volcano, and that the footprints were no more than 19,000 years old.
Meanwhile, the paleoanthropologists were trying to figure who left these tracks. Researchers found at least 24 distinct series of steps made by different individuals going in different directions, and have sorted out the age, gender, and whether the person was walking or running. Most of the footprints belonged to women and children walking together, they found.
"Knowing that somebody was walking through this exact spot, at this moment in time, thousands of years ago," Kevin Hatala, another co-author on the study, told the Post, "it does provoke lots of questions about what were these people doing there, who were they with?"
The region where the footprints were found is hot and dry. Water from the closest lake is undrinkable, and the active volcano visible from the spot still “spews strange, silver lava into the valley below.” The desolate conditions might have be the same for the prehistoric humans who walked this path.
Previously, ancient human footprints were found in Lateoli, another site in Tanzania with 3.6 million year-old footprints. Two sites in South Africa have tracks from 120,000 years ago, while Australia's Willandra Lakes has 700 fossil footprints from 20,000 years ago, according to National Geographic.
To protect the area, the Tanzanian government has placed barbed wire around the site, and the research team created 3-D scans of the footprints.
“God forbid anything happens to that site,” Liutkus-Pierce told National Geographic, “[but] we essentially have the ability to replicate it with 3-D printing.”