Stone Age Chinese began cultivating rice more than 7,700 years ago by burning trees in coastal marshes and building dams to hold back seawater, converting the marshes to rice paddies that would support growth of the high-yield cereal grain, researchers plan to report today.

New analysis of sediments from the site of Kuahuqiao at the mouth of the Yangtze River near Hangzhou provides the earliest evidence in China of such large-scale environmental manipulation, experts said.