'Lost' river that ran through Thar Desert 172,000 years ago found

Researchers have found the evidence of a "lost" river that ran through the central Thar Desert, near Bikaner, as early as 172 thousand years ago, and may have been a life-line to human populations enabling them to inhabit the region.

The findings, published in the journal Quaternary Science Reviews, represent the oldest directly dated phase of river activity at Nal Quarry in the central Thar Desert.

The study by researchers from The Max Planck Institute for the Science of Human History in Germany, Anna University in Tamil Nadu, and IISER Kolkata indicates that Stone Age populations lived in a distinctly different Thar Desert landscape than we encounter today.

This evidence indicates a river flowed with phases of activity dating to approximately up to 172 thousand years ago, nearby to Bikaner, Rajasthan, which is over 200 kilometres away from the nearest modern river.

These findings predate evidence for activity in modern river courses across the Thar Desert as well as dried up course of the Ghaggar-Hakra River, the researchers said.

The presence of a river running through the central Thar Desert would have offered a life-line to Paleolithic populations, and potentially an important corridor for migrations, they said.

The researchers noted that the potential importance of 'lost' rivers for earlier inhabitants of the Thar Desert have been overlooked.

"The Thar Desert has a rich prehistory, and we've been uncovering a wide range of evidence showing how Stone Age populations not only survived but thrived in these semi-arid landscapes," said Jimbob Blinkhorn from The Max Planck Institute for the Science of Human History.

"We know how important rivers can be to living in this region, but we have little detail on what river systems were like during key periods of prehistory," Blinkhorn said.

Studies of satellite imagery have shown a dense network of river channels crossing the Thar Desert, according to the researchers.

"These studies can indicate where rivers and streams have flowed in the past, but they can't tell us when," explained Professor Hema Achyuthan of Anna University.

"To demonstrate how old such channels are, we had to find evidence on the ground for river activity in the middle of the desert," Achyuthan said.

The team studied a deep deposit of river sands and gravels, which had been exposed by quarrying activity near the village of Nal.

The researchers were able to document different phases of river activity by studying the different deposits.

"We immediately saw evidence for a substantial and very active river system from the bottom of the fluvial deposits, which gradually decreased in power through time," Achyuthan said.

The researchers used a method called luminescence dating to understand when quartz grains in the river sands were buried.

The results indicated that the strongest river activity at Nal occurred at approximately 172 and 140 thousand years ago, at a time when the monsoon was much weaker than today in the region.

River activity continued at the site between 95 to 78 thousand years ago, after which only limited evidence for the presence of a river at the site, with evidence for a brief reactivation of the channel 26 thousand years ago, the study found.

The river was flowing at its strongest during a phase of weak monsoonal activity in the region, and may have been a life-line to human populations enabling them to inhabit the Thar Desert, the researchers said.

The timeframe over which this river was active also overlaps with significant changes in human behaviour in the region, which have been linked with the earliest expansions of Homo sapiens from Africa into India, they said.

"This river flowed at a critical timeframe for understanding human evolution in the Thar Desert, across South Asia and beyond," said Blinkhorn.

"This suggests a landscape in which the earliest members of our own species, Homo sapiens, first encountered the monsoons and crossed the Thar Desert may have been very different to the landscape we can see today," he added.