The story of phosphorus spans the globe and vast tracts of human history. The race to mine phosphorus took people from the battlefields of Waterloo, which were looted for the bones of fallen soldiers, to the fabled guano islands off Peru, the Bone Valley of Florida, and the sand dunes of the Western Sahara. Over the past century, phosphorus has made farming vastly more productive, feeding the enormous increase in the human population. Yet, as Egan...