Scientists say they have tentatively established the oldest date yet for anatomically modern Homo sapiens: 195,000 years--almost 40,000 years older than the oldest remains dated so far.
The dates come from volcanic rocks found in the vicinity of two partial skulls that were discovered near the Omo River in southern Ethiopia in 1967. When the skulls, known as Omo I and Omo II, were unearthed from under about 80 meters deep by Richard Leakey and colleagues, they were estimated to be about 130,000 years old. But dating methods then were uncertain.
Now a team led by geochronologist Ian McDougall of the Australian National University in Canberra has used argon-argon dating on volcanic deposits directly below where the skulls were found. Although the researchers could not find datable material in the layer right above the skulls, they say other geological data indicate that the fossils aren't much younger than the rocks.
The new dates also help resolve the issue of whether Omo I and Omo II were contemporaneous. Omo I looks more "modern" than Omo II. But the dating, says McDougall, whose report appears in this week's Nature, seems to confirm the prevailing view that the two skulls "simply reflect morphological variation in Homo sapiens at that time." McDougall also points out that the Omo hominids may be among the earliest modern humans. According to genetic studies, our earliest direct ancestors are estimated to have evolved around 195,000 years ago. Co-author Frank Brown, a geologist at the University of Utah's College of Mines and Earth Sciences, adds that finding Homo sapiens from that far back shows there is a major time lag between the origin of our species and the time we developed a true culture, around 50,000 years ago. Paul Renne of the Berkeley Geochronology Laboratory in California, who dated 160,000-year-old hominid fossils in Herto, another part of Ethiopia, says the McDougall team are "probably correct" in their belief that the Omo hominids aren't much younger than 195 thousand years. He says it would be nice if they could confirm the age by dating the layer just above the skulls, but they "did as well as one can with a difficult dating challenge."