Incredibly, the researchers extrapolate the approximately 400 confirmed sites to an estimated 20,000 to 30,000 earthwworks across the region. Pärssinen and his colleagues believe these structures are evidence of an interconnected, multicultural civilization that thrived deep within the Amazon between 600 BCE and 850 CE—a population of millions who dramatically altered the rainforest’s ecosystem. If correct, however, those calculations would imply that tens of millions of people inhabited rainforests once thought to be pristine wilderness. Pärssinen and his coauthors, instead, found compelling evidence that the Aquiry left a profound mark on the Amazonian ecosystem. “The civilization also affected ancient Amazonia’s carbon production and carbon balance,” he said, “which should be better accounted for in future climate models.”