Billions of people today owe their lives to a single discovery now a century old. In 1909 German chemist Fritz Haber of the University of Karlsruhe figured out a way to transform nitrogen gas—which is abundant in the atmosphere but nonreactive and thus unavailable to most living organisms—into ammonia, the active ingredient in synthetic fertilizer. The world’s ability to grow food exploded 20 years later, when fellow German scientist Carl Bosch developed a scheme for implementing Haber’s idea on an industrial scale.