Harappan Civilization May Have Been Killed by 200 Year Drought

Not good news for the southwest USA, for sure, where we've been in a long-term drought going on 50 years now.  Snail shells tell the tale...

From nature.com

Two-hundred-year drought doomed Indus Valley Civilization

Monsoon hiatus that began 4,200 years ago parallels dry spell that led civilizations to collapse in other regions.

• Emma Marris

03 March 2014

 

The decline of Bronze-Age civilizations in Egypt, Greece and Mesopotamia has been attributed to a long-term drought that began around 2000 bc. [Well attested.]  Now palaeoclimatologists propose that a similar fate was followed by the enigmatic Indus Valley Civilization, at about the same time. Based on isotope data from the sediment of an ancient lake, the researchers suggest that the monsoon cycle, which is vital to the livelihood of all of South Asia, essentially stopped there for as long as two centuries.

 

The Indus Valley, in present Pakistan and northwest India, was home to a civilization also known as the Harappan Civilization. It was characterized by large, well-planned cities with advanced municipal sanitation systems and a script that has never been deciphered. But the Harappans seemed to slowly lose their urban cohesion, and their cities were gradually abandoned.

The link between this gradual decline and climate has been tenuous because of a dearth of climate records from the region. So Yama Dixit, a palaeoclimatologist at the University of Cambridge, UK, and her colleagues examined sediments from Kotla Dahar, an ancient lake near the northeastern edge of the Indus Valley area in Haryana, India, that still seasonally floods.

The team assigned ages to sediment layers using radiocarbon dating of organic matter. In various layers, they collected the preserved shells of tiny lake snails (Melanoides tuberculata), which are made of a form of calcium carbonate (CaCO₃) called aragonite. The team also looked at the oxygen in the argonite molecules, counting the ratio of the rare oxygen-18 isotope to the more prevalent oxygen-16.