Modern deforestation in the Acre state of Brazil has allowed the discovery of more than 450 of large geometrical geoglyphs or enclosures, providing evidence for how indigenous people lived in the Amazon before European people arrived in the region. 

The structures are ditched enclosures that occupy roughly 13000 square kilometres. Their discovery challenges assumptions that the rainforest ecosystem has been untouched by humans. The function of ditched enclosures is still not understood. Archaeologists recovered very few artefacts during excavations within them, so they are believed to unlikely be villages. The layout doesn’t suggest they were built for defensive reasons. It is thought they were used only sporadically, perhaps as ritual gathering places.

The archaeologists extracted soil samples from a series of pits dug within and outside of the geoglyphs. From these soils, they analysed the phytoliths – a type of microscopic plant fossil made of silica, to reconstruct ancient vegetation; charcoal quantities, to assess the amount of ancient forest burning; and carbon stable isotopes, to indicate how ‘open’ the vegetation was in the past.

The researchers were able to reconstruct 6000 years of vegetation and fire history around two geoglyph sites. They found that humans heavily altered bamboo forests for millennia and small, temporary clearings were made to build the geoglyphs. Instead of burning large tracts of forest, people transformed their environment by concentrating on economically valuable tree species such as palms. The biodiversity of some of Acre’s remaining forests may have a strong legacy of these ancient “agroforestry” practices.

(after Live Science, EurekAlert, Daily Mail Online, Popular Archaeology, University of Exeter & Jenny Watling)