EUGENE, OREGON—According to a statement released by the University of Oregon, researchers led by Lucas Silva of the University of Oregon think that patches of fertile soil in the Amazon rain forest known as Amazonian Dark Earths (ADEs) could have been created through natural processes, rather than through human intervention, as has been previously suggested. Silva and his team members analyzed and dated soil samples collected near the confluence of the Solimoes and Negro rivers in northwestern Brazil, and found that calcium, phosphorous, and other nutrients in the soil likely originated from fires upstream. These minerals, which are found in ADEs, could have been transported to other areas through the river flooding that occurred after a long dry period between 8,000 and 4,000 years ago. Otherwise, the researchers suggest, it would have taken a large, sedentary population thousands of years of soil management work to transform the land to support agriculture. It is more likely, they argue, that people identified and settled in areas with arable soil and then developed soil management techniques. Read the scholarly article about this research in Nature Communications. For an alternative explanation of the origins of ADEs, go to "Dark Earth in the Amazon."