2014, vol. 40 (2): 219–232 Amazonian Dark Earths in the context of pre-Columbian settlements Beata Golińska Jagiellonian University, Institute of Archaeology; ul. Gołębia 11, 31-007 Krakow, Poland; e-mail: [email protected] © 2014 Authors. This is an open access publication, which can be used, distributed and reproduced in any medium according to the Creative Commons CC-BY 4.0 License requiring that the original work has been properly cited. Received: 4 September 2013; accepted: 14 June 2014 Abstract: Important information about pre-Columbian Amazonian settlement and economy provide Amazo- nian Dark Earths (ADE), black or brown soils characterized by the presence of charcoal in high concentrations, with highly elevated nutrients and organic matter and higher pH level. Usually ADE are related to large concen- trations of ceramics, stone artifacts and animal remains. The main factor for the initiation of ADE formation was the long-lasted, fully sedentary pre-Columbian settlement. Its size and a form can be correlated with traces of historical human habitation. Thus, these sites can reflect the social organization of a specific group. Therefore, ADE studies can bring much valuable information concerning pre-Columbian settlement in Amazonia. Keywords: Amazon, anthropogenic soils, pre-Columbian settlement, Amazonian Dark Earths, terra preta INTRODUCTION are weathered and acidic and almost completely devoid of essential nutrients (Mann 2007: 373). Studies on the environment and its modifications Almost the entire area of Amazonia is covered by the former communities of tropical forest ar- by an acidic and infertile laterite soil: red soils (ul- eas play a unique role in understanding of Am- tisols, color result from the accumulation of iron) azonian prehistory. The most evident argument and yellow laterite soils (characterized by the for the presence of large groups of people in the presence of a high concentration of hydrogen ions Amazonia are “black earths” (Amazonian Dark and a high acidity). A large number of iron com- Earths – ADE), especially their variation – terra pounds and the acidity make laterite soils condi- preta. ADE are considered as a result of past Indi- tions practically not suitable for efficient cultiva- an actions, who more or less consciously enriched tion. The major divisions of tropical soils include the soil with charcoal, organic waste and ceramics also ferralsols (ferralitic soils) characterized with shards. Therefore, ADE are proof of the existence a low natural fertility. The exceptions are for ex- of large and numerous prehistoric settlements in ample fluvisols (fluvial soils), mineral-rich alluvi- Amazonia as well as the artifacts themselves. al deposits located in the Amazon River Basin. In 1989, the Polish Society of Soil Science has Study area – environment proposed a system of soil classification with ma- and soils of Amazonia jor divisions into seven hierarchic soil units in- Moist tropical forests, extremely rich and varied, cluding: I) lithogenic, II) autogenic, III) semi-hy- hide poor and barren ground. Amazonian soils, drogenic, IV) hydrogenic, V) alluvial soil, VI) exposed to continuous heavy rainfall, are examples saline and VII) anthropogenic. For the purposes of intensive leaching processes. As a result, they of this article it will discuss only the section VII http://dx.doi.org/10.7494/geol.2014.40.2.219 ISSN 2299-8004 | e-ISSN 2353-0790 | Wydawnictwa AGH 220 Golińska B. including soils transformed as result of past hu- AMAZONIAN DARK EARTHS – man activities, including burial, partial removal, Terra preta cutting and filling, waste disposal and irrigated agriculture (anthrosols). Amazonian Dark Earths are ubiquitous at archae- Anthropogenic soils, formed under the influ- ological sites in Amazonia and cover 6–18 000 km2 ence of human activities are typologically trans- of forested areas of lowland Amazonia (Woods formed. Different profile horizons, the lack of some et al. 2009: 1). Most of the sites are located in terras genetic levels or the presence of new, bio-phys- firmes (uplands, forested area above the season- ico-chemical and hydrological transformations al inundations), on the headlands, on the banks as a result of municipal agriculture and industry of watercourses or lakes, or on várzea (“flooded lead to the division of two orders: culture earth forest”), annually flooded plains (Kämpf et al. soils, transformed under the influence of intensive 2003: 78, Kern et al. 2004: 19). management and industrial earths and urban soils. Early scholars and explorers reported densely Anthrosols, are formed as a result of direct (irri- populated villages extending along the river run- gation, addition of organic waste or wet-field cul- ning sometimes for several kilometers and a thick tivation) or indirect (through the modification of network of roads connecting big settlement clus- vegetation, deforestation) human activities. Such ters located more inland. Research indicates that processes can be intentional or random. Deliberate terra preta can reflect the location of those settle- actions aimed at improving the quality of the soil ments (Woods et al. 2004: 3). Thus, came the idea are likely to occur simultaneously with the spread of the anthropogenic nature of these soils. Spec- of agriculture (Woods 2003). Fertilizers were used ification of terras pretas, high concentration of during the reign of the pharaohs in Egypt. Hes- charcoal and the frequent occurrence of pottery iod and Xenophon mentioned that Greeks were fragments and stone artifacts seem to confirm fertilizing their fields to improve their fertility. In this hypothesis. Carthage, bird droppings were used as a fertilizer. In comparison to the otherwise infertile Am- Also Cato and Columella, the Roman authors rec- azonian soils ADE are highly fertile (Glaser et al. ommended pigeon droppings as an ideal fertilizer. 2004: 9) and can be found practically on all of its Guano was also highly appreciated by the Incas. territory. The problem with its origins and the role In Amazonia, among the best-known exam- that they have played in the cultural processes in ples of anthrosols are Amazonian Dark Earths the pre-Columbian period for years have been dis- (ADE), very dark in color, with a great amount of cussed by a broad group of archaeologists, anthro- broken pot sherds, highly elevated levels of pH pologists, geographers, and soil scientists. Many and increased concentrations of organic matter. theories considered the process of formation of These characteristics make them extremely fer- those extremely fertile soils have been proposed, tile. ADE encompasses two specific types, a clas- from purely random natural processes to inten- sic form: terra preta – “black earth” (also known tional activities including soil fertilization. Most as a terra preta do índio – „Indian black earths”; researchers agree with the view that terra preta is terra preta antropogenica – “anthropogenic black anthropogenic in nature, although it is not clear earth” or terra preta arqueologica – “archaeologi- if it was formed intentionally or unintentionally cal black earth”; Petersen et al. 2001: 86, Sombroek (Neves et al. 2003: 29). Either way, it was created et al. 2002: 2, Kämpf et al. 2003: 78, Lehmann as a result of past human activities. et al. 2003: 105, Woods et al. 2004: 3, Maris 2006: One of the most essential problems in ADE 624) and terra mulata (“brown earth”; Fraser et al. studies is a different approach to these soils and 2009: 229, Kern et al. 2003: 71, Myers et al. 2003: different ways of their research. The lack of one 18, Woods et al. 2009: 1). Both of these soils are valid definition or even a clear indication of its characterized by a high content of charcoal, which characteristics poses many problems. Researchers, gives them the typical dark brown or black color. who map and identify ADE typically rely on the Scholars calculated that ADE contains 64 times classification of the lands used in archeology and more charcoal than other surrounding soils (Gla- their interpretations; which, unfortunately, are ser et al. 2004, Thayne et al. 2009: 279). rarely consistent with contemporary knowledge https://journals.agh.edu.pl/geol Amazonian Dark Earths in the context of pre-Columbian settlements 221 of soil science. However, the archaeologists are where all post-production waste was accumulated experts in understanding and interpretation an- (Woods et al. 2009:4). thropogenic soils, associated with human activi- Friedrich Katzer, author of pioneering works ties occurring at sites in Amazonia. Soil scientists, on ADE, in his work on the geology of the Ama- on the other hand, focus on the horizons seen in zonia (1903) stated that the “most characteristic the soil profiles, considering anthropogenic char- richness (of Amazonia) lies in the soil” (Woods acteristics as perturbations and interferences. In et al. 2009: 8). Based on the results of three contrast, archaeologists focus on the visible and years of field research (1895–1898) he estimated structural features in the profiles of anthropo- that the area between the drainages of Tapajós genic formation, perceiving soil levels as pertur- and Curuá Una is covered by “Schwarze Erde” bations and disruptions. They focus mainly on (Woods et al. 2009: 8), which have completely the internal features of ADE: changes in texture, different origins than chernozems from Central color, context, and filling. Traditional archaeolo- Europe (Woods 2003: 3). He stated those soils gy focuses on building chronology, by describing consist of a characteristic mixture of mineral profiles of small, but often deep ADE excavations deposits, carbonized plant material and partial- (Erickson 2003: 462). ly distributed organic substances. Moreover, the estimated content of organic matter was 15–20% The history of ADE studies (Woods 2003: 4). Because of its unique richness, Knowledge of the historical Amazonian commu- writes Katzer, ADE was used by indigenous com- nities and their farming methods is mainly based munities in the past, when the area was densely on historical records: early conquistadors, chron- populated (Woods 2003: 4).