ByFEB. 10, 2017
Credit: Jenny Watling
For centuries, the enigmatic structures remained hidden to all but a few archaeologists. Then in the 1980s, ranchers cleared land to raise cattle, uncovering the true extent of the earthworks in the process. More than 450 of these geoglyphs are concentrated within Acre State in Brazil.
Since the discovery, archaeological study of the earthworks and other evidence has challenged the notion that the rain forests of the Amazon were untouched by human hands before the arrival of European explorers in the 15th century. And while the true purpose of the geoglyphs remains unknown, a study published on Monday in The Proceedings of the National Academy of Sciences offers new insight into the lives of the ancient people who lived in the Amazon. Thousands of years before the earthworks were built, humans were managing the forests, using what appear to be sustainable agricultural practices.
“Our study was looking at the environmental impact that the geoglyph builders had on the landscape,” said Jennifer Watling, an archaeologist at the University of São Paulo, Brazil, who conducted the research while a student at the University of Exeter in Britain. “A lot of people have the idea that the Amazon forests are pristine forests, never touched by humans, and that’s obviously not the case.”
Dr. Watling and her team reconstructed a 6,000-year-old environmental history of two geoglyph sites in the Amazon rain forest. To do this, they searched for clues in soil samples in and around the sites. Microscopic plant fossils called phytoliths told them about ancient vegetation. Bits of charcoal revealed evidence of burnings. And a kind of carbon dating gave them a sense of how open the vegetation had been in the past.
About 4,000 years ago, people started burning the forest, which was mostly bamboo, just enough to make small openings. They may have planted maize or squash, weeded out some underbrush, and transported seeds or saplings to create a partly curated forest of useful tree products that Dr. Watling calls a “prehistoric supermarket.” After that, they started building the geoglyphs. The presence of just a few artifacts, and the layout of the earthworks, suggest they weren’t used as ancient villages or for military defenses. They were likely built for rituals, some archaeologists suspect.
Dr. Watling and her colleagues found that in contrast with the large-scale deforestation we see today — which threatens about 20 percent of the largest rain forest in the world — ancient indigenous people of the Amazon practiced something more akin to what we now call agroforestry. They restricted burns to site locations and maintained the surrounding landscape, creating small, temporary clearings in the bamboo and promoting the growth of plants like palm, cedar and Brazil nut that were, and still are, useful commodities. Today, indigenous groups around the world continue these sustainable practices in forests.
“Indigenous communities have actually transformed the ecosystem over a very long time,” said Dr. Watling. “The modern forest owes its biodiversity to the agroforestry practices that were happening during the time of the geoglyph builders.”