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Wednesday, February 19, 2020

Doomed civilisations

Studies on Lonar crater show that a long dry spell may have led to the collapse of several societies, including Indus Valley.

Written by Vivek Deshpande | Published: March 16, 2014 12:46:32 am
Lonar crater has sediments deposited over 5,70,000 years Lonar crater has sediments deposited over 5,70,000 years

Studies on Lonar crater show that a long dry spell may have led to the collapse of several societies, including Indus Valley.

An Indo-German study of several millennia-old sediments deposited in Lake Lonar in Buldana district of Maharashtra has concluded that prolonged drought conditions stretching over several centuries may have been the main cause for the collapse of several civilisations, including the Indus Valley Civilisation. The decline of Bronze-Age civilisations in Egypt, Greece and Mesopotamia have also been attributed to a long-term drought that began around 2000 BC.

The study to ascertain climatic changes over the ages was jointly conducted by a team from the Indian Institute of Geomagnetism in Mumbai and the German Research Centre for Geoscience in Potsdam, Germany, led by professor Nathani Basavaiah and paleoclimatologist Sushma Prasad.

The findings were recently published in Journal Earth and Planetary Science Letters, published in Amsterdam.

Basavaiah told The Sunday Express, “Among the most popular reasons that are believed to have caused the decline of Indus Valley Civilisation was the shrinking of the Saraswati river. Our study has established that there was a prolonged drought, with the drying beginning nearly 4,200 years ago. It became very intense between 3,500–3,000 years ago, and the people could not cope with the conditions.”

These results, according to him, are supported by the wide-spread formation of hematite, an oxidised magnetic mineral found in the sediments at Lonar. “The intensity of rainfall is characterised in the amount of hematite found in the sediments.”

“The findings link the decline of the enigmatic Indus Valley Civilisation to the crumbling of the other Bronze Age civilisations in Egypt, Greece and the Akkadian Empire in Mesopotamia, all at the same time, indicating that these other civilisations were also hit by this prolonged drought,” said Basavaiah.

The disappearance of Saraswati coincides with a prolonged drought, but needs to be verified with stacked sedimentary profiles representing the entire Indian subcontinent, he said.

Lonar, a meteor crater lake, was the focus of the study as it is lies in the core zone of the Indian monsoon and has preserved sediments that have been deposited into it over a period of 5,70,000 years. Till around two years ago, it was believed that the lake was formed 50,000 years ago, but a recent study published in the journal Geology claims the lake was formed approximately 5,70,000 years ago.

“The 1.8 km-diametre crater represents the only known terrestrial impact site with target rocks composed entirely of basalt, which is a rich source of magnetite and titanomagnetite. Any variation of this primary magnetic mineral due to climate and environmental changes is bound to be recorded in the sediments. That’s why it serves as an important testimony to climate changes,” Basavaiah explained.

If a lack of adequate rainfall did spell the end of the Indus Valley civilization, says Basavaiah, “it is an example — and there are other examples of this — of how ancient societies have had to contend with climate.

How old is the Lonar crater?

Recent results, reported in the journal Geology by scientists from Australia, USA and Austria, suggest from the most precise radiometric ages that the Lonar crater was formed at 5,70,000 years ago. This robust age determination discarded the earlier young age estimation of somewhere between 12,000 and 62,000 years for the Lonar impact event. Basavaiah says, “Efforts are now being made to confirm the age of the impact event at Lonar using palaeomagnetic technique.”

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