Archaeology and ethnography demonstrate a human origin for Amazonian Dark Earths

Archaeological research provides clear evidence that the widespread formation of Amazonian Dark Earths (ADEs) in tropical lowland South America was concentrated in the Late Holocene, an outcome of sharp demographic growth that peaked towards 1000 BP. In their recent paper, however, Silva et al. propose that the high fertility of ADE is not of anthropic origin but instead the result of alluvial deposition starting in the Middle Holocene (8200-4200 cal BP). In order to support this argument, they marshal data and observations from a single expanse of ADE, the archaeological site of Caldeirão, and disregard or misread other studies of ADEs in the Central Amazon region. Silva et al.'s claim, an epilogue to ‘geogenic’ models laid to rest over 40 years ago, also dismisses research showing how long-term anthropic soil enrichment occurs as a result of daily practices at contemporary indigenous settlements. Here we critically review Silva et al.’s analysis and affirm that, like most ADEs, Caldeirão has anthropic soil horizons formed by burning, deposition, and reworking of refuse associated with indigenous settlement activities between 2500 and 500 BP.