Ancient earthworks built in the Amazon have been revealed due to deforestation and modern technologies. The findings have been discovered in the western Brazilian Amazon by Brazilian and UK experts. The area had been covered by trees for centuries, but modern deforestation along with satellite images have revealed 450 of these large geometrical geoglyphs in Acre state built about 2,000 years ago. Their discovery is significant since it contradicts the theory that the rain-forest ecosystem has never been touched by humans.

The structures are ditched enclosures measuring up to 36 feet wide, 13 feet deep and 300-1,000 feet in diameter. They are marked by a highly formalized structure made of geometrical circles and squares.

The team analysed soil samples from various points in the inside and outside of the geoglyphs. In particular they analysed phytoliths, a type of microscopic plant fossil, to reconstruct ancient vegetation. They also analysed charcoal quantities, to assess the amount of ancient forest burning, and carbon stable isotopes, to see how open the vegetation was.

The function of the sites has not yet been defined, but they were probably not used for habitat or defensive reasons. They might have been places for ritual gatherings and ceremonies.

Researchers also conducted studies around two sites to define to what extent the region was forested when the geoglyphs were built, resulting in the reconstruction of 6,000 years of vegetation and fire history. Their findings were stunning, as it turns out humans had altered the natural growth of bamboo forests for millennia and made clearings to build the geoglyphs.

They concentrated on various tree species, such as palms, used for food and building, and avoided deforestation of larger areas with the use of fire. Researchers believe that today’s forests bear traces of these ancient agroforestry practices.

According to Dr Jennifer Watling, post-doctoral researcher at the Museum of Archaeology and Ethnography, University of Sao Paolo, who carried out the research when she was studying for a PhD at the University of Exeter, the extent of human intervention on the forests in the recent years is much larger. The practices performed in antiquity did not lead to forest degradation and that should lead to wiser and more sustainable forms of intervention consistent with indigenous practices.

The study was published in the journal Proceedings of the National Academy of Sciences.

The full article will be released in the Proceedings of the National Academy of Sciences of the USA and involved researchers from the universities of Exeter, Reading and Swansea (UK), São Paulo, Belém and Acre (Brazil). The research was funded by the Arts and Humanities Research Council, National Geographic, and the Natural Environment Research Council Radiocarbon Facility.