Scientists from the India Institute of Technology in Kharagpur, and the Archaeological Survey of India, have uncovered evidence that the Indus Valley Civilisation is at least 8,000 years old, and that pre-Harappan civilisation existed for at least 1,000 years before this. They also believe climate change ended the civilisation about 3,000 years ago.
     Anindya Sarkar, head of the department of geology and geophysics at IIT-Kharagpur, says: "We have recovered perhaps the oldest pottery from the civilisation. We used a technique called 'optically stimulated luminescence' to date pottery shards of the Early Mature Harappan time to nearly 6,000 years ago and the cultural levels of pre-Harappan Hakra phase as far back as 8,000 years."
     The team's excavations at an unexplored site - Bhirrana - also yielded large quantities of animal remains like bones, teeth, and horn cores of cow, goat, deer and antelope.
     The researchers believe that the Indus Valley Civilisation spread over a vast expanse of the sub-continent. While earlier phases were represented by pastoral and village farming communities, and mature Harappan settlements were highly urbanised with organised cities, a developed material and craft culture, and regular trade with Arabia and Mesopotamia, the Late Harappan phase is characterised by large-scale de-urbanisation, drop in population, abandonment of established settlements, lack of basic amenities, violence, and even the disappearance of the Harappan script.
     The study shows that the pre-Harappan humans started inhabiting this area in a climate favourable for settlement and agriculture.
     "The monsoon was much stronger between 9000 years and 7000 years ago, and probably fed these rivers making them mightier with vast floodplains," explains Arati Deshpande Mukherjee of Deccan College, which helped analyse the finds.
     The researchers say that, with the declining monsoon, the Indus Valley people shifted their crop patterns from large-grained cereals like wheat and barley to drought-resistant species like rice. As the yield diminished, the organised storage system of the Mature Harappan period gave way to more individual household-based crop processing and storage systems, acting as a catalyst for the gradual decline of the civilisation rather than any abrupt collapse.

Edited from Times of India (29 May 2016)