Initially, the monsoon-drenched rivers the researchers identified were prone to devastating floods. Over time, monsoons weakened, enabling agriculture and civilization to flourish along flood-fed riverbanks for nearly 2,000 years.
“The insolation — the solar energy received by the Earth from the sun — varies in cycles, which can impact monsoons,” Giosan said. “In the last 10,000 years, the Northern Hemisphere had the highest insolation from 7,000 to 5,000 years ago, and since then insolation there decreased. All climate on Earth is driven by the sun, and so the monsoons were affected by the lower insolation, decreasing in force. This meant less rain got into continental regions affected by monsoons over time.”
Story: Charles Choi, LiveScience | Photo: Joseph Bord, Shutterstock