Terra preta is a phenomenon found across all four types of ecosystems, although it is rare in the upland forests closer to the Andes. Terra preta (“black earth”), also called Terra Preta do Indio (“Indian black earth”) is the Brazilian name for certain highly fertile dark earths in the Amazon region created by indigenous peoples. Terra preta soils exist across a wide range of parent soil types — red or yellow kaolinite ferralsol, acrisol, sandy podzol, and terra preta is distributed throughout a wide range of Amazonian environments — black and whitewater ecosystems, bluff edges and headwaters, floodplains and terra firme. It is estimated that 10% of the Amazon Basin is terra preta. The area of terra preta already mapped is immense — twice the size of the UK.
The properties and behavior of terra preta defy scientific understandings. Terra preta does not form naturally out of compost, even where composting is intentional. Contemporary settlements, even indigenous ones, do not create terra preta.
Yet, terra preta seems to continuously regenerate itself. In Brazil, there are sites where prehistoric terra preta has been intensively farmed for nearly forty years with no addition of any fertilizer. Some scholars suggest that terra preta essentially represents a “living organism” because of its capacity to regenerate itself.
Archaeologists have surveyed the distribution of terra preta and found it correlates with the places in which conquistador Francisco de Orellana’s chroniclers described seeing cities. Radiocarbon dating shows that the terra preta seems to start around the time of Christ, perhaps a few hundred years earlier. This is the same time that archaeologists first see complex polychrome pottery and evidence of mound building in the Beni and on Marajó Island. The abundance of pottery shards found in every deposit of terra preta, and the traces of ancient roads connecting them, demonstrate that terra preta correlates with intensive human occupation.
Organic matter in terra preta averages 40 to 50 cm deep, but may be as deep as one to two meters (!) Radiocarbon dating demonstrates the extremely fast rate of terra preta formation — a meter of soil produced in just a few decades. It is calculated that 24500 tons of silt and algae or 9000 tons of mulch would be required to cover one meter of topsoil over one hectare, so this which implies high labor investment and complex social organization.
In the modern world, intensive agriculture and population growth are associated with ecological destruction and soil decline – but in the Amazon, as a result of farming and as a result of population growth, the soils grew richer, not poorer. Terra preta today also appears to be preserving plant species that cannot survive elsewhere in the Amazon, thus helping to preserve and promote biodiversity.
Besides creating continuing soil fertility, terra preta has another benefit that its creators cold not have foreseen: it helps to sequester carbon dioxide.
The technology for creating terra preta seems to have been lost by present-day indigenous populations of the Amazon. Special inoculations of microorganisms were involved, but those bacterial cultures and the technologies for using them are today lost. But when the mystery of creating terra preta is solved, it may be one of the greatest gifts of the Amazonian native peoples to the world.
#sachamama in action