One of the greatest civilizations that ever existed collapsed some 4000 years ago, and now geologists believe they may know why: climate change. By analyzing snail shells from the ancient lake Kotla Dahar in Haryana, India, researchers could decipher how much rain fell when the snails lived thousands of years ago. The results, published this week in Geology, demonstrate a sudden weakening of the summer monsoon that led to drought—and the likely abandonment of the Indus Valley civilization’s major cities. Although climate change has been suggested as a cause of decline in the past, there was never any direct evidence until now.
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