The conclusions came from mapping carried out using sensors equipped with optical lidar (light detection and distance measurement) technology. Attached to a drone or on board an aerial vehicle, the device emits thousands of laser pulses per second, and with each pulse, calculates a distance measurement. “It’s almost like an X-ray,” explains geographer Vinicius Peripato, a doctoral student at the National Institute for Space Research (Inpe) and first author of the study. Thanks to the high resolution of the equipment, he and his colleagues were able to see the topography of the Amazon forest under the tree canopy using data processing.

From above, in already deforested areas of the western part of the Amazon, it is possible to observe huge geometric shapes on the ground, called geoglyphs. From the 2000s onwards, geoglyphs began to be seen through satellite images, both by scientists and amateurs, using Google Earth. “It would have been possible to identify hundreds of such structures, especially in western Amazonia,” says biologist Luiz Aragão, head of the Department of Earth Observation and Geoinformatics at Enppi, advisor to Peribato and coordinator of the scientific article.

Over the past 20 years, excavations by archaeologists have shown that the geometric shapes were sites of religious significance. Knowing the existence of these structures, Peripato and his colleagues created a hypothesis that other traces of human occupation could exist beneath the forest canopy. Starting to look for them was a challenge.

Originally, lidar sensor data intended for biomass estimates did not have sufficient resolution for archaeological observations. “Previous tests indicated the possibility of these structures, but nothing was precise,” Peripato explains. Building on this hypothesis, the group developed a method to actually clear the forest and improve terrain aspects. “It worked, and fortunately we found 24 buildings that were previously unknown.” The equipment covered an area of ​​5,315 square kilometers of the Amazon, equivalent to 0.08% of the forest.

Excited by this discovery, the researcher developed a mathematical model to estimate how many and where other similar geomorphs exist in the region, taking into account a series of still unknown variables. He compared the data provided by the lidar sensor with information from 937 other known archaeological structures, and using this model, he calculated that there were at least 10,272 pre-Columbian structures still undiscovered, as many as 23,648 structures in the entire forest. 6700 square kilometers. . The distribution of 53 domesticated plant species, used for food, has been mapped in previous forest inventories and can serve as an indicator of the presence of archaeological structures in the vast Amazon region.

“It was a mission that required a multidisciplinary team and the use of the latest technologies to implement,” says Aragão. The dating of the as-yet undiscovered geoglyphs has been estimated based on the existing archaeological literature on these structures, but can only be confirmed when excavations are carried out and material is collected for analysis.

“It is an important article that confirms what archaeologists have said for years: There were many people living in the Amazon region in the past“, comments archaeologist Eduardo Goes Neves, from the Museum of Archeology and Ethnology of the University of São Paulo (MAE-USP). “These people lived there and also modified the forest,” he says. Human presence in the area dates back to about 12 thousand years ago. For For some experts, the Amazon is a biocultural heritage influenced by nature itself and by the people who lived and continue to live there.

“The changes made to the forest are very valuable information so that we can better understand what the structure of a biome that has been occupied for thousands of years looks like, what is the resilience of that area and how it seeks to return to its original form,” Peripato comments. “With climate change processes, understanding how the forest works is extremely important.”

Nieves says that a large portion of the geoglyphs that are still preserved are on ecologically protected lands inhabited by indigenous people. “It is the indigenous people who maintain the structures amid the progress of agribusiness and the devastation taking place in the Amazon,” the researcher says. For him, the presence of indigenous people has always been present throughout Brazil, is very ancient and contributed to the creation of the country’s biomes. “You can’t separate their history from Brazil’s history.”