Study Further Investigates Human Evolution

By dating artifacts from one of the oldest Middle Stone Age archaeological sites worldwide, UC Berkeley geologists have unearthed the possibility that humans were fashioning advanced tools far earlier than originally thought.

The study, published in the December issue of Geology, may push the emergence of modern humans back to almost 300,000 years ago-100,000 years earlier than what the results of previous studies showed.

Researchers used argon-argon dating, a relatively accurate form of isotope dating developed by the late UC Berkeley physicist John Reynolds, to determine the age of ash surrounding obsidian tools found in volcanic sites in Ethiopia. The tools were thought to be used by early people.

The work builds on studies from an excavation done in the 1970s, which dated the same tools using the less precise method of potassium-argon dating, said Paul Renne, a UC Berkeley associate adjunct professor of earth and planetary science, director of the Berkeley Geochronology Center and co-author of the study.

Leah Morgan, the other co-author of the study and a UC Berkeley graduate student in earth and planetary science, traveled to Ethiopia for a different research project in 2006, at which time she performed a preliminary examination of Kulkuletti and Gademotta, the two archaeological sites.

In 2007, she and Renne returned to compare the sites and study their geologic strata. By correlating the strata and volcanic ash from both sites, they determined that the sites had been hit by the same volcanic eruption.

At Gademotta, a number of obsidian tools had been driven to the surface over time by erosion.

"We found tons of tools," Renne said. "The area is so littered with them that you can't walk without stepping on them­-they're just all over the place."

Although no human remains were found at the site, which is high up on a volcanic ridge, the tools were clearly used for hunting animals and cutting and scraping meat, Renne said. He added that many of the tools resembled Native American arrowheads.

"They're amazingly advanced," Renne said. "They're really well-made, very finely crafted, and they have all the diversity of function that Middle Stone Age artifacts have, which are much, much more recent than these."

The quality of the materials-as well as the agility and intelligence of their creators-likely contributed to the high-quality workmanship, he said.

But Renne and Morgan did not have a research permit to collect the tools. They were only able to inspect the geologic strata and remove volcanic ash that surrounded the tools, Renne said.

"All we were doing was looking at rocks," he said.

Morgan said the previous study probably did not fully de-gas the samples, resulting in an inaccurate age.

"There were some pretty serious flaws with the original dating work," Renne said.

When considering the new study, scientists should not rule out the possibility that a species other than Homo sapiens made the tools, Morgan said.

And even if modern humans are the toolmakers, the study merely reveals how much data is lacking in the geologic record, Renne added.

"If somebody can really prove convincingly that humans and only humans were capable of making these kinds of tools, and by inference that Homo sapiens go back 300,000 years, that would be super cool, really exciting­-and also not that surprising," he said.

Tags: EARTH AND PLANETARY SCIENCE