Monday, August 2

Kolkata: Climate change wiped out ancient river, city, says IIT study

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The extinction of Dholavira — the biggest and most spectacular Harappan city in present-day Kutch district of Gujarat — was caused by the drying-up of a massive river that originated in the Himalayan glaciers in prehistoric times because of climate change, research by a team of scientists from IIT Kharagpur suggests.

The river that ran through the desert of the Rann of Kutch was one of the main sources of sustenance for Dholavira. The scientists, led by geologists from IIT Kgp, said this was the first time that the existence of a perennial river located by a Harappan site was being vouched for.

The findings, which have excited historians and archaeologists across the world, have been published in the Wiley Journal of Quaternary Science, a peer-reviewed academic journal published on behalf of the Quaternary Research Association. It covers research on any aspect of quaternary science, an inter-disciplinary field of study focusing on the Quaternary period, which encompasses the last 2.6 million years.

The scientists said the river dried up because of climate change, when the glacier feeding it melted away. They said the river might remind one of the mythical Saraswati, which is also said to be lost, but is definitely not the same. The researchers have not been able to christen it yet, but have concluded that it might have been a distributary of the Indus, or might have been a “paleochannel” that ran beside Dholavira. A paleochannel is a remnant of an inactive river or stream channel that has been filled or buried by younger sediment.

The river existed since prehistoric times but the civilisation started proliferating from 5,500 years ago and died about 3,800 years ago. The research has concluded that when the residents of Dholavira sensed that the river was gradually drying up, they adopted an advanced water-conservation system that helped them to survive for the last 1,700 years.

While the research was led by Anindya Sarkar and his team from the department of geology and geophysics, the other agencies that collaborated were the Archaeological Survey of India (ASI), Deccan College PGRI Pune, Physical Research Laboratory, and the department of culture, government of Gujarat.

“Our data suggest that prolific mangroves grew around the Rann, when the river existed in the near southern margin of the Thar desert. This is the first direct evidence of the glacier-fed river, quite like the Saraswati, in the vicinity of the Rann,” Sarkar said.

Ravi Bhushan and Navin Juyal from PRL, Ahmedabad dated the carbonates from human bangles, fish otolith and molluscan shells by accelerator mass spectrometer and confirmed the dating of the site. From potsherds and other remains found at the site, the researchers have also concluded that the Dholavirans were probably the original inhabitants of the region and had a fairly advanced level of culture even at their earliest stage. The study indicates that the city expanded for 4,400 years followed by an abrupt decline. Researchers R S Bisht and Y S Rawat from the ASI, who originally excavated the site, concluded that the decline was evident in the degeneration of architecture, craftsmanship and material culture of Dholavira.

Arati Deshpande Mukherjee of the Deccan College said: “We have evidence from high-resolution oxygen isotopes in snail shells Terebralia palustris, which typically grow in mangroves and was a source of food for the Dholavirans.” Researchers also concluded that the snail isotopes suggested that the mangrove was fed by a glacial river that existed near the site. The drying of the river coincided with a mega drought period that is known in history as the Meghalayan drought. “Indeed, Dholavira presents a classic case for understanding how climate change can increase future droughts,” added Sarkar.


Source: Times of India

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