An international team of researchers has completed an extraordinary study that reveals the presence of thousands of undetected earthworks hidden beneath the dense cover of the Amazon rainforest in South America.
Based on their discovery of about two dozen earthworks in the Amazon found during aerial surveys, the researchers estimate that somewhere between 10,000 and 24,000 unknown earthworks must still be waiting to be discovered within the Amazon Basin. It is believed that these earthworks in the Amazon were left there by indigenous peoples who lived in the region before the era of Spanish and Portuguese occupation and colonization.
Cutting-Edge Technology Reveals Earthworks in the Amazon
In a landmark research paper published in Science, the archaeological researchers explained how they reached this stunning conclusion. Hoping to find evidence of at least some undiscovered Amazon earthworks, the researchers analyzed data collected from airborne studies of the Amazon biomass in the northern, central and southern regions of the world’s largest rainforest. This data was intriguing because it was obtained from aerial surveys that used LiDAR laser scanning technology to develop detailed physical maps of the Amazon’s forest floor.
LiDAR is short for “light detection and ranging,” and this scanning-and-imaging technology can use reflected laser light to trace the exact contours of any landscape, even those hidden beneath dense layers of vegetation. LiDAR laser can penetrate a thick forest canopy like that found in the Amazon rainforest without being deflected, which means the images of the ground it produces will show all ground features exactly as they are, with no distortion.
Study co-lead author Vinícius Peripato, a doctoral candidate in remote sensing at Brazil’s National Institute for Space Research, explained in an interview with Scientific American why his team decided to examine previously collected LiDAR images from the Amazon.
“We thought, ‘Maybe the ground can tell us some stories about the archaeology as well,” he said when discussing the earthworks in the Amazon. “At the beginning, it was a complete shot in the dark; we had no idea if we would find anything.”
The Amazon rainforest may host more than 10,000 sites with pre-Columbian earthworks, according to a groundbreaking study published today in the journal @ScienceMagazine. pic.twitter.com/IKORPwAtgC
— Amazon Conservation Team (@AmazonTeamOrg) October 6, 2023
Finding the Amazon Earthworks with LiDAR Imagery
When the researchers began pouring over the LiDAR images, they were delighted to discover telltale signs that allowed them to identify 24 unique Amazon earthwork sites. The earthworks they saw included geoglyphs (mounds depicting animals, humans, gods or abstract shapes), ponds, wells, ring ditches and other assorted structures created by the piling up or removal of significant quantities of rock and soil.
Even though indigenous people have been living in the Amazon for more than 12,000 years, the majority of these earthworks in the Amazon were built between 1,500 and 500 years ago. This was during the latter stages of the Pre-Columbian era.
The total acreage displayed in the LiDAR images represented only about one-tenth of one percent of the Amazon’s total area. Nevertheless, using computer models the researchers felt confident projecting their findings to the rest of the region.
Assuming a relatively universal distribution of these Amazon earthworks, they estimate that there would have to be at least 10,000 structures still awaiting discovery in various unexplored sections of the Amazon, although the number could certainly be much higher. These estimates were adjusted to account for soil quality (sandier Amazon forest soil wouldn’t be suitable for making earthworks), proximity to water sources (population densities would shrink as people got farther from fresh water) and geography (some landscapes would have been less desirable for settlement and earthworks production because of excessive rockiness or hilliness).
To put the numbers in perspective, as of now only about 1,000 earthworks in the Amazon have been discovered during ground-level surveys of the area. If the latest estimates are right, this would only represent between four and 10 percent of the total number of earth structures that actually exist.
LiDAR technology is helping researchers to identify unknown earthworks in the Amazon. The image shows LiDAR date outputs of the many layers of the terrain. ( Vinicius Peripato )
LiDAR Reveals the Secrets of Civilization in the Amazon
In the past, the only way to find earthworks and other evidence of civilizational activity in the Amazon was through onsite exploration. However, the density of the Amazon forest cover and vegetation made this an incredibly difficult task and one that was impossible to undertake rapidly.
But the development of LiDAR technology has been a game-changer. The relevance of LiDAR technology to archaeology was most clearly demonstrated in recent surveys taken of Maya lands in Mexico and northern Central America, during which archaeologists discovered networks of interconnected Maya cities hidden inside dense forests.
“We thought the Maya area was very well studied, but when we started to do LiDAR work [there], we had lots of surprises,” Takeshi Inomata, an archaeologist at the University of Arizona who was not involved directly in the latest study, told Scientific American . “I think there will be more of those surprises in Amazonia.”
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Example of earthworks found in the Amazon. ( Utrecht University )
Recent studies have suggested that population levels in the Pre-Columbian Amazon were higher than had been previously estimated. It is believed that as many as eight to 10 million people had made their homes there before the Spanish and the Portuguese arrived in the Americas. The discovery of so many hidden Amazon earthworks is consistent with this conclusion, as the ubiquitous nature of these structures reveals that human settlements must have existed everywhere inside the Amazon’s borders.
The earthworks in the Amazon were not the only signs of ancient civilization revealed through the LiDAR analysis. In the relatively tiny patches of 2,052 square miles (5,315 square kilometers) of Amazon land they looked at, the researchers identified the remains of a fortified village, several other settlement sites and various religious or ceremonial structures. The village featured an expansive central plaza and would have been included as part of a larger cluster of urban settlements in the southern Amazon.
In addition, they also identified 53 tree species known to have been domesticated by the indigenous peoples of the Amazon located in the vicinity of the various earthworks. This shows that settlers were actively engaged in organized agricultural activity , intentionally growing trees that would produce edible fruits or wood to be used for building or fires. Such activity would have been necessary for stable civilizations to have developed in the ancient Amazon, where the environmental challenges would have been immense.
Unimaginable Amazonian Archaeological Treasures Await Discovery
Archaeologists have always been fascinated by the earthworks left behind by ancient peoples, all around the world. They once covered nearly every part of the landscape in the Americas, having been constructed in huge numbers for a broad range of ceremonial, spiritual and artistic purposes. In most areas of the Americas only a small percentage of these earthworks still exist, having been destroyed by farmers who saw them as a nuisance and plowed them over.
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But they would remain largely untouched and protected inside the thick Amazon forest , hidden from detection for centuries. Thanks to the arrival of LiDAR technology, archaeologists will finally have the opportunity to study them.
If indeed thousands of such structures are ultimately discovered, they will yield a bounty of information about how indigenous peoples survived in the Amazon, modifying the dense and inhospitable forest environment to make it more habitable for humans.
“The massive extent of archaeological sites and widespread human-modified forests across Amazonia is critically important for establishing an accurate understanding of interactions between human societies, Amazonian forests, and Earth’s climate,” the study authors wrote in their Science paper. “Amazonian forests clearly merit protection not only for their ecological and environmental value but also for their high archaeological, social and biocultural value, which can teach modern society how to sustainably manage its natural resources.”