1.9-million-year-old discovery rewrites the story of human evolution

An archaeological site in the Jordan Valley is rewriting the timeline of early human migration. New research shows that 'Ubeidiya is at least 1.9 million years old, placing humans in the region hundreds of thousands of years earlier than previously believed. The revised dating makes 'Ubeidiya, alongside Dmanisi in Georgia, one of the oldest known sites of early human activity outside Africa. The findings suggest that ancient human populations, using different types of stone tools, had already spread into the Levant during a crucial early period of human expansion beyond Africa.

The research was 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. By combining three advanced dating methods, the team established a more reliable timeline for 'Ubeidiya, a site that has played an important role in research on human evolution.

Their findings indicate that the site is at least 1.9 million years old, making it one of the earliest known locations where ancient humans lived outside their African homeland.

The 'Ubeidiya Formation has attracted scientific attention for decades because of its early evidence of the Acheulean stone tool tradition. This technology is known for large tools shaped on both sides, including hand axes. The site also contains a rich collection of animal fossils, representing species originally associated with Africa and Asia, including several that are now extinct.

Despite its importance, researchers have struggled to establish exactly when early humans occupied the area. Previous estimates generally placed 'Ubeidiya between 1.2 million and 1.6 million years old, but those dates relied on comparisons with other archaeological and geological evidence rather than direct measurements.

To resolve the uncertainty, the researchers collected new samples from the site and analyzed them using three complementary dating techniques. Each provided an independent source of evidence about the age of the ancient deposits.

The first technique, called cosmogenic isotope burial dating, uses rare isotopes that form when cosmic rays interact with rocks exposed at Earth's surface. After the rocks become buried, these isotopes decay at known rates. Measuring what remains allows scientists to estimate how long the rocks have been underground.

The researchers also investigated evidence of Earth's ancient magnetic field recorded in sediments deposited at the bottom of a lake. As these sediments accumulated, they preserved the orientation of the magnetic field at the time. Comparing these records with known magnetic reversals showed that the deposits formed during the Matuyama Chron, a period that began more than two million years ago.

A third technique involved fossilized shells from Melanopsis, a genus of freshwater snails found within the sediment. Using uranium-lead dating, the team was able to establish a minimum age for the geological layers containing the ancient stone tools.

The combined evidence indicates that 'Ubeidiya dates back at least 1.9 million years, significantly changing the timeline of early human settlement beyond Africa.

This places the Jordan Valley site at approximately the same age as Dmanisi in Georgia, another major location for understanding early human migration. The similarity in age suggests that ancient human populations were expanding into different regions around the same time.

The findings also raise intriguing questions about how these early migrations unfolded. Evidence from the two sites suggests that different groups of ancient humans may have carried distinct stone tool technologies out of Africa during overlapping periods.

These included the Oldowan tradition, associated with relatively simple stone tools, and the more sophisticated Acheulean tradition, known for carefully shaped tools such as hand axes. Rather than spreading in a single technological sequence, these different approaches to toolmaking may have traveled beyond Africa at roughly the same time as separate groups of early humans entered new environments.

The researchers also had to explain an unexpected complication in their results. Initial measurements of cosmogenic isotopes suggested that some rocks were approximately three million years old, considerably older than indicated by the site's magnetic, fossil, geological, and archaeological evidence.

The sediments had undergone a complicated history of repeated deposition, burial, exposure, and movement within the Dead Sea rift and the surrounding landscape. Some of the material had been buried long before it was eventually transported and deposited again near the ancient lake at 'Ubeidiya.

This recycling meant that the geological history recorded by certain rocks extended much farther into the past than the formation of the archaeological layers themselves.

"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."

The results establish 'Ubeidiya as one of the oldest known centers of early human activity outside Africa. They also suggest that the movement of our ancient relatives into new territories was already underway 1.9 million years ago, potentially involving multiple populations with different toolmaking traditions.