Two Iowa State researchers are part of an international team of geologists and archaeologists which two years ago found the oldest known accurately dated fossil remains of a human ancestor of our own genus, “homo.”

The 2.33 million year old upper jaw found on a barren hillside near Hadar in northern Ethiopia was also found with several stone chopping tools, making this the oldest firmly-dated association of stone tools with a human ancestor.

Carl Vondra, professor and chair of ISU’s geological and atmospheric sciences department, and Tesfaye Yemane, an ISU graduate student and native of Ethiopia, traveled to Ethiopia in 1993, 1994 and again this past January to research the rock surrounding the fossil.

Their contribution to the discovery was to help establish the date for the find and the physical conditions of the hominid at the time of its death by researching and reconstructing the “paleoenvironment” of the area.

Vondra said they are not certain whether the fossil should be classified as homo erectus or homo habilis, the two predominant ancestral species in our human genus, but it most probably belongs with one of them.

Their results were published in the December 1996 issue of the Journal of Human Evolution. According to this issue, “a broad consensus among paleoanthropologists holds that the ‘Homo’ originated in Africa sometime between two and three million years ago. However, a gap in the east African hominid fossil record spans the better part of this million-year interval.”

Analysis of the site itself, using a single-crystal argon laser probe, yielded an age of about 2.33 million years for the discovery, the journal reported.

Prior to this discovery, stated the article, the earliest undisputed date for a homo fossil find was about 1.9 million years.

The oldest accepted date for the association of a human ancestor with primitive tools prior to this find was about 1.85 million years.

Hadar is also the area in which the famous “Lucy” skeleton — the largely complete skeleton of a young adult female of the species Australopithecus afarensis, a hominid ancestor to the homo genus — was discovered more than 20 years ago.

Yemane is simultaneously investigating the paleoenvironment of Lucy and of the newly discovered homo fossil.

He said that about six months ago he discovered something new about the conditions in which Lucy died.

“Lucy actually died in a flood plain about one kilometer away from a meandering stream, perhaps as a result of a flood,” he said.

“The hardest part of the job in my field is identifying the layers and collecting all the data from the sediment. You have to measure the thickness, the flow directions, the transport mechanisms and the [physical or chemical] characteristics of the sediment deposits in the appropriate layer,” Yemane said

Two of the principal types of rock geologists working on such projects work with are sediment and basalt. Yemane said while sediment is quite good at preserving fossils, it is difficult to accurately date; in contrast, while basalt is not as good an environment for preserving fossil remains, it does lend itself much more readily to modern dating techniques.

Yemane said another challenging part of their job in Hadar that makes it interesting is the formation’s location in the middle of a rift-valley.

“The area is extremely tectonically-active; it is located at the conjunction of three continental plates, which are pulling apart from one another, creating this rift-valley, which widens at a rate of something like a centimeter per year,” he said.

During their last excursion to Africa this past January and February, Vondra and Yemane also found a new fossil site in the newly independent country of Erithrea, formerly a part of Ethiopia, and they plan on returning to that site next January to do more detailed work.