In 2023, a satellite-image model led archaeologists to 13 previously unknown Amazon geoglyphs, including one 444 metres across

For years, the Amazon rainforest was widely described as a pristine wilderness with no large-scale human settlement before European colonization. That description has been challenged by a growing body of research, including a 2023 study that used machine learning to identify likely locations of undiscovered archaeological sites in the southern Amazon basin. Researchers from the University of Missouri and the University of Tulsa used a random forest algorithm, a machine-learning method, to identify environmental patterns associated with known ancient settlements, then used those patterns to flag unsurveyed areas likely to contain similar sites. What exactly did the model find

The study identified 13 previously unknown geoglyphs, including a circular earthwork measuring 444 metres in diameter. The 2023 peer-reviewed study, titled "Predicting the geographic distribution of ancient Amazonian archaeological sites with machine learning," was conducted by researchers at the University of Missouri and the University of Tulsa and published in the journal PeerJ. According to the study, its best-performing model achieved an area under the curve (AUC) of 0.91 and an overall classification accuracy of 88 percent when tested with spatial cross-validation, figures the earlier draft rounded imprecisely to "91% accuracy.

Led by anthropologist Robert Walker, the research team used a random forest algorithm to determine which environmental variables, including soil phosphorus concentration, distance to rivers, rainfall patterns, and temperature, were most closely associated with the locations of known archaeological sites. According to the study, ancient builders tended to settle in areas with fertile soil, reliable river access, and a dry season suitable for clearing forest by burning. The model used these associations to generate probability maps identifying other locations with similar characteristics that had not yet been surveyed, this replaces the earlier version, which incorrectly stated the model was "trained on satellite imagery" in one paragraph and then denied that in the next.

The model flagged unsurveyed forest areas in Brazil and Bolivia as having a high probability of containing earthworks. Subsequent deforestation in parts of those areas revealed previously undocumented geoglyphs and ditched enclosures. The study cites earlier research estimating that constructing an average geoglyph required about 8,000 person-days of labor.

Broader implications for conservation debates

The findings also bear on a long-running debate about the ecological history of the Amazon. Some researchers have argued that parts of the region were sparsely populated before European contact, while this view has been challenged by studies that have found evidence of large-scale societies in the Amazon region long before Europeans arrived. A 2018 study, "Pre-Columbian earth-builders settled along the entire southern rim of the Amazon," published in Nature Communications by Jonas Gregorio de Souza and colleagues, documented more than a thousand earthwork sites along the southern rim of the Amazon.

A separate 2022 study, "Lidar reveals pre-Hispanic low-density urbanism in the Bolivian Amazon," published in Nature by Heiko Prümers and colleagues, used LiDAR to reveal pre-Hispanic low-density urbanism with plazas and pyramids in the Bolivian Amazon. These studies show that new technology has helped researchers document pre-Columbian structures and settlements that were previously hard to detect.

Why should this matter


These discoveries add to evidence that parts of the Amazon supported organized, large-scale societies prior to European contact. One caveat is that these geoglyphs and earthworks often only become visible because the surrounding forest has been cleared.

Researchers have noted that illegal logging and ranching in the Amazon have exposed ancient ruins and geoglyphs that would otherwise have remained hidden, underscoring that many of these discoveries have resulted from increased deforestation in the region. Researchers are hoping to use non-invasive methods, such as LiDAR, to locate other geoglyphs and ruins without further deforestation.