Terra Preta is not a result of a natural process. It was made by ancient Indians populating Amazon area. It seems that this practice has been cultivated for centuries since some areas rich with the dark soil contain pottery, dated 500 years, whereas other areas contain tools estimated to be older than 7,000 years!
The beneficial effects of biochar were not only used in Amazonia. Biochar was also found in parts of Africa and Indonesia. In Japan, biochar is used for ages to improve the nutrient profile of the soil for bonsai potting. Some researchers argue that only poor soils could be improved, good soils could face an opposite effect.