As more and more multibillion-dollar projects for sequestering carbon dioxide (CO2) deep within the Earth seek financial support, human-formed fertile black soils in the Amazon basin suggest a cheaper, lower-tech route toward the same destination. Scattered patches of dark, charcoal-rich soils known as terra preta (Portuguese for "black earth") are the inspiration behind international efforts that are investigating how burying biomass-derived charcoal, or "biochar," could boost soil fertility and transfer a sizeable amount of CO2 from the atmosphere into safe extended storage in topsoil. Although burial of biochar is just beginning to be tested in long-term field trials, studies of Amazonian terra preta reveal that charcoal has the potential to lock up carbon in soils for centuries.