Mental Floss

Geoglyphs Are Evidence of Ancient Farming in the Rainforest

Kate Horowitz
Edison Caetano
Edison Caetano / Edison Caetano

Our complicated relationship with the rainforest may be much older than we thought. Archaeologists writing in the Proceedings of the National Academy of Sciences say the creators of ancient South American earthworks had also been farming and clearing the Amazon for millennia before Europeans arrived. The most striking evidence for this manipulation of the landscape? Hundreds of geoglyphs discovered across the region, revealed by deforestation.

For a long time, the rainforest appeared lush and undisturbed, and we assumed it had always been that way. Then during the last century, cattle ranchers began cutting down more and more trees to make room for their livestock. When the sawdust had settled, massive shapes could be seen carved into the soil. Archaeologists discovered more than 450 of the geoglyphs in Brazil’s Acre State alone.

Edison Caetano

Diego Gurgel

Edison Caetano

Lead author Jennifer Watling is an archaeologist at the University São Paulo. She said the glyphs’ discovery created quite a stir. “A lot of people have the idea that the Amazon forests are pristine forests,” she told The New York Times, “never touched by humans, and that’s obviously not the case.”

What was the case, then? To find out, Watling and her colleagues collected soil samples from two of the glyph sites. They sifted through the soil, picking out microscopic plant fossils and pieces of charcoal, then used carbon dating to approximate the age of each tiny bit of evidence.

They've been working on this research for a while; in the multilingual video below, from 2013, listen to the researchers explain some of their techniques.

The evidence told a story about the people who lived and worked in the forest around 4000 years ago. They had done some forest clearing of their own, burning sections of bamboo to open up space for farming. They likely grew maize or squash and collected food-bearing trees in one spot to create what Watling called a “prehistoric supermarket.” Once these forest farms were established, they began digging out the glyphs, which were likely used in religious rituals.

Unlike today’s industrial logging and clearing, the glyph-builders’ agriculture was sustainable in nature. Their farms and burn areas were small and contained, and permitted the surrounding wilderness and trees to keep on growing.

“Indigenous communities have actually transformed the ecosystem over a very long time,” said Watling. “The modern forest owes its biodiversity to the agroforestry practices that were happening during the time of the geoglyph builders.”