When European researchers discovered part of a fossilized jaw in a Serbian cave, they suspected their finding could help solve some mysteries surrounding human evolution.

Almost seven years later, researchers at McMaster have played a key role unlocking at least one of the secrets the sample held: its approximate age.

The fragment, unearthed in 2006, was originally thought to be 130,000 years old. But findings published in a new article for the online journal PLOS ONE suggest it is much more ancient.

'It's important because it places a time on a very primitive human fossil in terms of European human fossils.'—Jack Rink, McMaster

“The age estimate is around 450,000 years, plus the uncertainty,” said Jack Rink, a McMaster earth scientist who helped to date the specimen. It could be as “young” as 397,000 years old and possibly older than 525,000 years.

“It's important because it places a time on a very primitive human fossil in terms of European human fossils,” Rink told CBC Hamilton.

Unlike proto-Neanderthals who resided in western Europe during the same period, the species was not cut off from Asia and Africa, he said. As a result, the mandible exhibits features that are very different from its western contemporaries.

“It's very robust. The size of the bone of the jaw that the teeth are set into is much larger than the type of mandible that we humans have,” Rink said.

“In Neanderthals, it's really much thinner.”

Cave diggers

Researchers from the University of Belgrade started excavating the cave where the fragment was found in 2004.

Jack Rink is a professor of earth sciences at McMaster University. (McMaster University)

Once, while the scholars were away, looters attempted their own dig, presumably looking to make big bucks from finding buried paleo-anthropological treasure, Rink said.

Ironically, the plunderers helped the professional out, in a way.

“Within 10 centimetres of where the looters left it, they [the researchers] found the mandible.”

The dating game

Working in conjunction with European and other Canadian researchers, Rink and McMaster physicist Jeroen Thompson used three separate dating techniques to estimate of the age of the fossil.

One of those tests — called electron spin resonance analysis — was conducted in a McMaster lab.

The process, Rink said, involved grinding up goat and bear teeth that were found near the fossil, and adding radiation to the product. He cross-referenced the rate at which the radiation in the enamel depleted with radiation levels in the cave, giving his team a rough idea as to the fossil's age.

Under normal circumstances, Rink said, he'd get graduate students to run the tests, but none were available when the work needed to get done.

For that, the scientist considers himself a bit lucky.

“It was kind of fun,” he laughed. “I got to do it myself.”