[0:01]Four thousand years ago, the Harappan civilisation thrived along the Indus River in modern-day Pakistan.
[0:13]Yet by 1800 BC, they had abandoned their cities for small villages in the Himalayan foothills.
[0:25]No one has been able to explain the mysterious migration until now.
[0:45]The Harappans were a Bronze Age culture. They built large cities that were architecturally very planned. They had impressive water management structures. It's a good example of what I call a Goldilocks civilization. It appears that the Harappans were the beneficiary of a favorable climate window when the monsoons were not too strong so that you can practice the inundation agriculture.
[1:21]These sediments record the history of human impacts on land.
[1:29]We had to find a place to recover those sediments, that history in sediments, so we had to core, take cores offshore Pakistan, and we also had to move on land to understand exactly how the landscape changed where Harappans lived.
[1:50]This is a core from the Arabian Sea, and we're looking to understand the chemical composition of this core and to extract from it foraminifera.
[2:09]The whiter ones are more rich in calcium carbonate, which is indicative of Forams. The darker, the redder ones indicate more sediment coming from land. And the alternation, it's an indicator of climate changes. By studying the chemistry and DNA of these forams, scientists can find clues to the Earth's ancient climate.
[2:43]The sediment is also analyzed for isotopes that reveal its age.
[3:04]We found out that the winter monsoon increased at the time that the summer monsoon decreased.
[3:16]That provided them a push to migrate from the Indus Valley and also pull, a magnetic pull toward the foothills of Himalaya where the winter rain increased. They abandoned their inundation agriculture for rain agriculture. They didn't have art, they didn't build cities. They forgot how to write, but they still lived for another millennium doing subsistence agriculture.
