An image of a geoglyph from the air.

Environmental Impact of the Pre-Columbian 'Geoglyph Builders' in Western Amazonia

Professor José Iriarte

The unexpected discovery of immense geometrically patterned earthworks called 'geoglyphs' among the terra firme rainforests of western Amazonia is radically changing our notion of past human societies in this region of the Amazon. Over 400 of these spectacular geometric earthworks have been found across eastern Acre state, Brazil. Prior to the onset of large-scale deforestation in the 1980s, Acre state was completely blanketed by terra firme humid rainforest, assumed by most tropical ecologists to be pristine or virgin. Only after large-scale deforestation, did these previously hidden earthworks become visible. These earthworks comprise circles, squares, and other geometric shapes, between 90 and 300m diameter. Most occur on inter-fluvial uplands atop a 150–200m plateau. Their purpose, and scale of environmental impact associated with their construction, is still debated. Funded by National Geographic Society and in collaboration with archaeologist Denise Schaan we have started a project to investigate what was the past impact of the 'Geoglyph Builders' on this region of Amazonia and what is the modern legacy of their ancient land use. To tackle these questions we are using a multi-proxy approach, combining analyses of pollen, phytoliths, stable carbon isotopes, and charcoal, from radiocarbon-dated soil profiles and lake sediments from eastern Acre, which will be able to capture the rise and fall of the 'Geoglyph-Building' culture. Funded by AHRC, PhD student Jennifer Watling is currently conducting her dissertation on this project.