Modern humans’ family tree just got older.
New research by Frank Brown, U professor of geology and geophysics, and his colleagues has re-dated fossils of human skulls at 195,000 years old.
In 1967, the Homo sapiens’ skulls found in Kibish, Ethiopia were thought to be about 130,000 years old. New research at the same site pushed that date back by about 65,000 years.
“These are the oldest-known Homo sapiens that have been dated,” Brown said.
The skulls were found between two dated layers of rock that were 104,000 years old and 196,000 years old, give or take 5,000 years. The older rock was found about 10 feet below the skulls burial place, while the newer rock was found 160 feet above the skulls. Brown says erosional surfaces in the rock sequence indicate that the skulls are from the older timeframe.The dating is also consistent with dark- rock layers of sediment found on the Mediterranean Sea floor.
These rocks were deposited when the Nile River flooded during climactic periods when rainy seasons were accentuated. These deposits are called sapropels, and Brown says they correlate very well with the time of deposition of the sediments at Kibish that contain the fossils.
This is because when rainfall was high in the Ethiopian highlands, it filled Lake Turkana so that sediments were deposited at Kibish, and at the same time flooded the Mediterranean with fresh water, forming the sapropels.
John Fleagle, distinguished professor of anatomical sciences at Stony Brook University and co-author of the study, said these fossils have been on the forefront of paleoanthropology for several decades, but no one was sure of the dates on them.
“It’s nice to take on a fairly focused problem and then go out and get some answers,” Fleagle said.
One of the reasons the new date is significant is that Homo sapiens’ cultural artifacts-such as tools and musical instruments-didn’t begin to look consistently modern until about 50,000 years ago, so Homo sapiens were without these for nearly 150,000 years, Brown said.
The tools found with the skulls were mostly “cobbles”-small stones that were roughly hewn for cutting, and possibly projectiles, like arrowheads, according to Fleagle. The cobbles came from a nearby riverbed, which shows that these Homo sapiens were opportunistic and didn’t travel much farther than their immediate area, Fleagle said.
“Perhaps the most confusing, and odd, part of this is that you have these very anatomically modern humans, but they’re using the same old stone tools. You might expect some dramatic change in culture to go along with this anatomical change, but you don’t see it until about 40,000 years ago,” Fleagle said.
Brown said the findings are also consistent with the time that Homo sapiens, or modern humans, genetically diverged from other species of humanoids.
“These aren’t staggeringly older than what we previously thought, but the important thing is that we finally know how old these skulls are,” Brown said.
Brown, Fleagle and Ian McDougall of the Australian National University, co-authored the research. It appeared in the journal Nature.