Terra Preta or dark soil is a unique form of soil which has been created through human activity. This anthropogenic soil has some unique properties; in addition to being incredibly fertile and retaining that fertility for hundreds of years, Terra Preta is also a form of carbon sequestration. Both of these traits have led to widespread interest in Terra Preta around the world, with some people even proposing that it could be used to create a carbon negative fuel, using an energy generation technique called gasification.
Before delving into all of the claims for Terra Preta, it may help to understand what, exactly, it is. Dark soils were noticed in the Amazonian basin by many early explorers, and as early as the mid-1800s, people were wondering where these soils came from. They were notably richer than neighboring soils, and they clearly had distinct properties which were identifiable even in this age of science. Investigation revealed that Terra Preta was heavily laced with bio-char, or charcoal, and some people theorized that it came from volcanoes.
In fact, closer analysis of the components of Terra Preta indicates that it was made by people, possibly the same pre-Columbian civilization which shaped large swaths of the rainforest. In addition to bio-char, Terra Preta also contains plant remains, manure, shards of pottery, and the remnants of fish. In a sense, Terra Preta is glorified compost, but it is extremely mineral rich and very deep in many parts of the Amazon.
To make Terra Preta, people used a technique called slash and char, in which sections of the forest were cleared and burned in partially smothered, low intensity fires to generate charcoal. This charcoal, in turn, locked in carbon instead of releasing it into the atmosphere, which explains why people are excited about the possibility of using Terra Preta as a carbon sequestration tool. In addition, the blended contents of Terra Preta make it very rich, encouraging beneficial bacteria and fungi to grow.
In theory, Terra Preta could be produced anywhere, and it could end up being a valuable tool for amending severely damaged soils. Widespread use of harsh chemical fertilizers around the world could be replaced by Terra Preta, which would also help to repair soils damaged by these chemicals. In addition, Terra Preta could be burned in gasification engines, potentially sequestering carbon while it creates energy. Gasification is an old technique for generating energy by burning biomass in controlled conditions which turns it into a form of gas; this gas can and has powered an assortment of vehicles.