New dating evidence indicates that Ubaydiya in the Jordan Valley is at least 1.9 million years old, making it one of the oldest known sites of early human activity outside Africa, alongside Dmanisi in Georgia. The revised age suggests that ancient human populations were already moving into the Levant hundreds of thousands of years earlier than previously thought, and that groups using different stone-tool traditions may have been expanding beyond Africa during the same broad period.
The study was led by Professor Ali Matmon of the Hebrew University of Jerusalem, Professor Omri Barzilai of the University of Haifa, and Professor Miriam Bellmaker of the University of Tulsa. By combining three dating methods, the team established a more reliable chronology for Ubaydiya, a site that has played an important role in research into human evolution.
Stone tools and fossils record early human activity
The Ubaydiya Formation has attracted scientific attention for decades because it contains early evidence of the Acheulean stone-tool tradition. This technology is associated with large, carefully shaped tools featuring double-sided geometries, including hand axes. The site also contains a rich collection of animal fossils representing species originally associated with Africa and Asia, some of which are now extinct.
Despite the site’s importance, researchers had struggled to determine precisely when early humans occupied the region. Previous estimates generally placed Ubaydiya between 1.2 million and 1.6 million years old. Those estimates were based on comparisons with other archaeological and geological evidence rather than direct measurements.
To address the uncertainty, the researchers collected new samples from the site and analyzed them using three complementary dating techniques. Each method provided independent evidence about the age of the ancient deposits.
The first method, cosmogenic isotope burial dating, relies on rare isotopes formed when cosmic rays interact with rocks exposed at Earth’s surface. Once the rocks are buried, the isotopes decay at a known rate. Measuring the isotopes that remain allows scientists to estimate how long the rocks have been underground.
The researchers also analyzed traces of Earth’s ancient magnetic field preserved in sediments deposited at the bottom of the lake. As the sediments accumulated, they recorded the orientation of the magnetic field at that time. Comparing these records with known magnetic reversals showed that the deposits formed during the Matsuyama period, which began more than 2 million years ago.
The third method used fossilized shells of Melanopsis, a freshwater snail found in the sediment. Uranium-lead dating of the shells allowed the researchers to determine a minimum age for the strata containing the ancient stone tools.
Together, the three approaches indicated that Ubaydiya is significantly older than previous estimates suggested.
A revised timeline for migration beyond Africa
The combined evidence indicates that “Ubaydiya dates back at least 1.9 million years and significantly altered the timeline of early human settlements beyond Africa.”
This places the Jordan Valley site at approximately the same age as Dmanisi in Georgia, another important location for studying early human migration. The similar ages suggest that ancient human populations were expanding into different regions at roughly the same time.
The findings also raise questions about how those migrations unfolded. Evidence from Ubaydiya and Dmanisi suggests that different groups of ancient humans may have carried different stone-tool technologies out of Africa during overlapping periods.
These technologies included the Oldowan tradition, associated with relatively simple stone tools, and the more sophisticated Acheulean tradition, known for carefully shaped implements such as hand axes. Rather than spreading as a single technological sequence, the different approaches to toolmaking may have been transmitted across Africa during the same general period in which separate groups of early humans entered new environments.
Explaining the 3-million-year-old dating signal
The researchers also had to account for an unexpected complication in the results. Initial cosmogenic-isotope measurements suggested that some rocks were about 3 million years old—much older than indicated by the site’s magnetic, fossil, geological and archaeological evidence.
Further investigation revealed why the measurements appeared inconsistent.
The sediments had experienced a complex history of deposition, burial, exposure and movement within the Dead Sea fissure and the surrounding landscape. Some material had been buried long before it was transported and redeposited near the ancient lake at Ubaydiya.
This recycling meant that the geological history recorded by an individual rock extended much further into the past than the formation of the archaeological layer itself.
The researchers explain:
“The exposure-build history revealed by the model suggests recycling of sediments that were previously deposited and buried in the rift valley and then redeposited along the Ubaydiya paleolake shoreline.”
By reconstructing the history of the complex deposit, the team reconciled the conflicting measurements and strengthened the evidence for the site’s revised age.
The results establish Ubaydiya as one of the oldest known centers of early human activity outside Africa. They also indicate that the migration of ancient human relatives into new environments was already underway at least 1.9 million years ago and may have involved multiple groups with different tool-making traditions.
Source: www.sciencedaily.com
