Unintentionally. People have been mixing biochar into soil for fertility since the beginning of agriculture with slash-and-burn, but terra preta is the result o

Unintentionally. People have been mixing biochar into soil for fertility since the beginning of agriculture with slash-and-burn, but terra preta is the result of waste dumps (human waste, ashes, bones, pottery, other garbage) in settlements composting, not something people were intentionally creating.