An archaeological site in the Jordan Valley known as 'Ubeidiya has been dated to at least 1.9 million years old, placing early humans in the region hundreds of thousands of years earlier than previous estimates and establishing it alongside Dmanisi in Georgia as one of the oldest known activity sites outside Africa.
Advanced Dating Methods Revise the Jordan Valley Timeline
Previous estimates generally placed 'Ubeidiya between 1.2 million and 1.6 million years old. Those earlier dates relied on comparisons with other geological and archaeological evidence rather than direct measurements.
To resolve the uncertainty, a research team led by Prof. Ari Matmon of the Hebrew University of Jerusalem, Prof. Omry Barzilai of the University of Haifa, and Prof. Miriam Belmaker of the University of Tulsa collected new samples from the site. They analyzed the material using three complementary dating techniques.
The first method, cosmogenic isotope burial dating, measures rare isotopes that form when cosmic rays strike rocks exposed at the surface. Once buried, these isotopes decay at known rates, allowing scientists to calculate how long the rocks have remained underground.
The second technique examined Earth's ancient magnetic field recorded in lake-bottom sediments. As sediments accumulated, they preserved the magnetic orientation of the period. Comparing these records with known magnetic reversals showed that the deposits formed during the Matuyama Chron, which began more than two million years ago.
A third technique involved uranium-lead dating of fossilized shells from Melanopsis, a genus of freshwater snails found within the sediment. This established a minimum age for the geological layers containing the ancient artifacts.
Acheulean Stone Tools and Extinct Animal Fossils
For decades, researchers have focused on the ‘Ubeidiya Formation due to its early artifacts representing the Acheulean stone tool tradition. This technology is known for large tools shaped on both sides, including hand axes.
Additionally, the location preserves a diverse assortment of animal fossils featuring taxa originally linked to Asia and Africa, alongside several now-extinct varieties.
The revised age suggests that ancient human populations were expanding into different regions around the same time as those at Dmanisi in Georgia. The data suggest that separate populations of prehistoric humans could have dispersed outside Africa bearing distinct stone tool industries during contemporaneous epochs.
These included the Oldowan tradition, associated with relatively simple stone tools, and the more sophisticated Acheulean tradition. Distinct communities of early humans may have ventured into unfamiliar landscapes carrying these varying toolmaking strategies simultaneously rather than sequentially.
Reconciling Conflicting Cosmogenic Isotope Measurements
The researchers also had to explain an unexpected complication in their results. Initial isotope-based measurements implied an age of roughly three million years for certain rocks, exceeding by a wide margin the dates derived from the location’s fossil, magnetic, archaeological, and geological records.
The layers of sediment had experienced an intricate sequence of burial, erosion, redeposition, and displacement across the Dead Sea rift zone and surrounding terrain.
Prior to their ultimate accumulation by the prehistoric lake at ‘Ubeidiya, portions of these materials had already been buried for a substantial period before undergoing subsequent transport and redeposition.
Because of this recycling process, the chronological history preserved within specific rocks stretched back far earlier than the actual creation of the archaeological strata.
As the researchers explained: “The exposure-burial history that emerges from the model implies recycling of sediments previously deposited and buried in the rift valley… and then redeposited along the 'Ubeidiya paleo lake shoreline.”
By factoring in this complicated sedimentary background, the investigators successfully resolved the discrepancies in their data and reinforced the validity of the site’s updated chronology.
Worth a look
