Likewise, weaker winds other times of year provide fewer nutrients, causing slightly less productivity in the waters offshore. “You can basically get fragments of DNA of nearly anything that’s lived there.”ĭuring winter monsoons, he notes, strong winds bring nutrients from the deeper ocean to the surface, feeding a surge in plant and animal life. “The seafloor near the mouth of the Indus is a very low-oxygen environment, so whatever grows and dies in the water is very well preserved in the sediment,” says Giosan. Once he and the team identified the season based on the forams’ fossil remains, they were able to then focus on deeper clues to the region’s climate: paleo-DNA, fragments of ancient genetic material preserved in the sediments. After taking core samples at several sites in the Arabian Sea, he and his group examined the shells of single-celled plankton called foraminifera (or “forams”) that they found in the sediments, helping them understand which ones thrived in the summer, and which in winter. That’s why Giosan and his team focused on sediments from the ocean floor off Pakistan’s coast. ”Įvidence for this shift in seasonal rainfall-and the Harapans’ switch from relying on Indus floods to rains near the Himalaya in order to water crops-is difficult to find in soil samples. Compared to the floods from monsoons that the Harappans were used to seeing in the Indus, it would have been relatively little water, but at least it would have been reliable. “As winter storms from the Mediterranean hit the Himalayas, they created rain on the Pakistan side, and fed little streams there. “Although fickle summer monsoons made agriculture difficult along the Indus, up in the foothills, moisture and rain would come more regularly,” Giosan says. 13, 2018, in the journal Climate of the Past. ![]() If you look at Syria and Africa, the migration out of those areas has some roots in climate change.”īeginning in roughly 2500 BCE, a shift in temperatures and weather patterns over the Indus valley caused summer monsoon rains to gradually dry up, making agriculture difficult or impossible near Harappan cities, says Liviu Giosan, a geologist at WHOI and lead author on the paper that published Nov. ![]() A new study from the Woods Hole Oceanographic Institution (WHOI) found evidence that climate change likely drove the Harappans to resettle far away from the floodplains of the Indus. ![]() Yet by 1800 BCE, this advanced culture had abandoned their cities, moving instead to smaller villages in the Himalayan foothills. More than 4,000 years ago, the Harappa culture thrived in the Indus River Valley of what is now modern Pakistan and northwestern India, where they built sophisticated cities, invented sewage systems that predated ancient Rome’s, and engaged in long-distance trade with settlements in Mesopotamia. Mohenjo-daro is an ancient Indus Valley Civilization city built around 2600 BCE that was abandoned after 1900 BCE.
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