Home to an estimated 16,000 tree species, the Amazon rainforest is an unparalleled hot spot for biodiversity. Western scientists once saw it as a leafy paradise relatively untouched by humans, but they have more recently recognized that human cultures have lived in large swaths of the rainforest for many millennia. Now, a new laser mapping and modeling study suggests thousands of human archeological sites remain undiscovered beneath the rainforest canopy.
The new study offers data to support what archaeologists working in the Amazon have argued for decades, says archaeologist Eduardo Neves of the University of São Paulo, who was not involved in the new research. “The Amazon is not a pristine forest,” he says. “It has been transformed by Indigenous people over millennia.” And it may help boost the claims of today’s Indigenous peoples to their traditional lands.
Lidar, an airborne laser mapping technology, has revolutionized archaeology in recent years. It allows researchers to “see” ancient humanmade structures covered by soil and dense vegetation—something satellite imaging can’t do. In 2021, for example, a to as far back as 3000 years ago in Mexico. And last year, researchers used the technology to describe ancient sites belonging to the Casarabe culture in the Bolivian Amazon.
In the Amazon, archaeologists have discovered humanmade earthworks—ditches, geoglyphs, ponds, and wells—with geometric shapes, some up to 1500 years old. The ancient people who created these earthworks also domesticated trees and crops, transforming the landscape and cultivating patches of dark, fertile earth. But systemically searching for such features simply wasn’t feasible until the advent of lidar.
Vinicius Peripato, a remote sensing scientist at Brazil’s National Institute for Space Research, wondered if the technology could peer beneath the entire, thickly forested Amazon Basin. He and more than 130 colleagues turned to publicly available lidar data spanning the entire basin in the country which had been previously collected by the Brazilian government to estimate rainforest biomass. “It was basically a shot in the dark,” Peripato says. When he started analyzing the data, geometric patterns such as squares and circles, resembling ancient earthworks, jumped out.
The more he looked, the more he found. Scanning 5315 square kilometers of lidar data, he and his fellow researchers identified more than 900 known earthworks throughout the basin. But they also discovered 24 previously unreported humanmade constructions all over the basin, including suspected ceremonial sites, fortified villages, and megalithic structures, some of rising only 1 meter or so above the forest floor.
However, their initial data covered only about 0.1% of the Amazon’s 6.7 million square kilometers. So, they combined the data of both the newly described earthworks and the previously reported ones to statistically predict how many more earthworks might be hiding in the basin. Taking into account such variables as temperature, precipitation, soil type, and distance to bodies of water, the researchers estimate that 16,187 earthwork sites remain undiscovered in the Amazon rainforest, they report today in Science. If they’re right, more than 90% of ancient earthworks remain concealed under the canopy.
The authors also found a significant relationship between 35 domesticated tree species—including Brazil nut, Pará rubber tree, murumuru, and cacao—and the probability of earthworks. That also fits with previous work showing domesticated tree species are more abundant near archaeological sites.
“People used to think [tropical areas] are really pristine forest,” says Takeshi Inomata, an archeologist at the University of Arizona who led the 2021 lidar study in Mexico. The new results suggest instead it “was very much inhabited space. … [It’s] one important step toward a much better understanding of [archaeology] in Amazonia.”
The team’s model estimates most of the unknown earthworks are concentrated in the southwest of the Amazon Basin. “That makes sense,” as most previously reported earthworks have been found there, says Daiana Travassos Alves, an archaeobotanist at the Federal University of Pará who was not involved in the study. The next step will be going into the field to see if researchers can find these predicted features, she says. “That’s going to be amazing.”
The results may also have implications for land rights for today’s Indigenous groups, a thorny topic in Brazil in recent years. Earthworks, the authors say, “serve as tangible proof of an ancestor’s occupation, way of life, and their relationship established within the forest.”
The Amazon rainforest is not only an ecological treasure, but also biocultural heritage, Neves says. “It’s really a result of the coevolution of Indigenous peoples and a forest over the millennia.”