Two Iowa State researchers are part of an international team that discovered the oldest firmly dated human fossil ever found along side stone tools.

A 2.33 million-year-old superior mandible, an upper jaw and palette, was uncovered in Hadar, Ethiopia.

The fossil and the primitive tools were originally discovered in November of 1994. The discovery of “Lucy” in 1974 prompted the continued search in the area for more fossils.

“Lucy” was the most complete example of the small brained, big jawed, upright walking Australopithecus afarensis, not known to have made stone tools. “Lucy” was recovered from rock layers dated between 3-3.4 million years ago.

The new discovery came from a geological layer approximately 700,000 years after the youngest known Australopithecus afarensis lived in Hadar.

Tesfaye Yemane, an Iowa State graduate student in geology, is helping construct the fossil’s environment. He has visited the site twice, each visit lasted approximately five to six months.

Carl Vondra, chief of Iowa State’s geological and atmospheric sciences department, also visited the site and is helping provide dating for the discovery.

He has been involved with field work projects since the 1960s.

The dating process is complicated. The crystal-laser fusion method of potassium-argon dating was used. This method provides “law of super position.” The volcanic ash layer is examined for potassium crystals and calculates how it decays to argon. The percentage is calculated with its half-life. This method is also used for precise dating of volcanic rocks.

Vondra said the tools were primitive choppers and flakes. These might have been used for crushing bones and removing flesh from the bones.

“There have been older stone tools found, some dating as far back as 2.6 million years, but these are the oldest tools found with an ancient fossil,” Vondra said. “The fossil, an ancestor to humans, may have made these tools.”

William Kimbel, Robert Walter and Donald Johanson, from the Institute of Human Origins, led the research team. They are trying to enter Ethiopia again for more research, but they are having difficulty getting permission. They were hoping to return next week, but they will have to delay their trip.

Vondra and Yemane hope to accompany the lead researchers again in January. Their search will be just north of Hadar in Eritrea. Their funding was provided by the National Geographic Society and the National Science Foundation.

A report on the discovery will be published in the December issue of Journal of Human Evolution.