**Abstract**

The anthropogenic origin of the Amazonian dark earths (*Terra Preta de Índio*) was first verified more than 70 year ago. However, the last 30 years have seen a massive wave of scientific investigation, public interest and an ever-expanding intensification of commercial activity toward all things connected to "*Terra Preta*." Today, the dominant concept, which drives current research, is that of binding atmospheric carbon with artificially concocted dark earths. The large-scale production of *Terra Preta* is said to be an effective tool in efforts to mitigate global warming. This text attempts to provide a history of the knowledge on Amazonian dark earths. It not only focuses on scientific aspects but also considers traditional indigenous knowledge. The position is taken that without indigenous knowledge, modern *Terra Preta* research would not exist; a view, which has profound implications for the ethical evaluation of all further, applied *Terra Preta Nova* research and commercial endeavors.

**Keywords:** Amazonia dark earths, *Terra Preta de Índio*, traditional indigenous knowledge, biochar, history of knowledge, global warming, carbon storage

## **1. Introduction**

Today, the term Amazonian dark earths (*Terra Preta de Índio*—Amazonian dark earths) refers to a dark soil most often found in limited zones in the lowland areas of Amazonia. These soils are, as a rule, concentrated near rivers and located on bluff zones above the floodplains (*várzea)* [1]. This unique soil has a significantly higher nutrient content, especially phosphorus and nitrogen, and a much higher pH value (around 6.7) when compared to other Amazonian soils [2, 3]. These soils are—as the name indicates—very visually dark and all of them contain some quantity of prehistoric material cultural remains. For this reason, all ancient *Terra Preta* sites are nowadays considered archeological in character and protected by Brazilian law.

According to Woods and Denevan [4], the *Terra Preta* sites cover an area of 0.1–0.3% (6000–18,000 km2 ) of the wooded Amazonian lowlands. As these soils are characterized by a long-term fertility, many of them are used by the local population, known as *caboclos*, in their agricultural practices [5–7].

The baseline, "non-*Terra Preta*," primary forest soils (especially oxisols) are generally extremely nutrient-poor, unless modified significantly through the

introduction of artificial fertilizer. These primary forest soils have a low pH value, which means they are extremely alkaline and suited for long-term agricultural use. The usual agricultural workaround, known as slash-and-burn, produces ash and coal, which provide for a temporary fertility. Immediately thereafter, the areas are generally abandoned as the soil fecundity declines and much waste in biomass and land use is the overall result in this highly inefficient approach [8].

The indigenous knowledge of *Terra Preta*, their location and qualities are still invaluable to the current discussion (for a more in-depth discussion on the subject see Manuela Carneiro da Cunha [9]). Simply taking into consideration solely peerreviewed scientific journal publications is, in our opinion, insufficient [4]. Such a limited approach creates a distorted perspective. Such a selective corpus might inspire the conclusion that only Western-based scientists and 21st century business concerns discovered and developed the fundamental benefits of the *Terra Preta de Índio.* Such a clearly simplified historically misinformed view might even be used for legitimizing claims to the economic exploitation of this important indigenous knowledge [10].
