The Ends of the World: Volcanic Apocalypses, Lethal Oceans, and Our Quest to Understand Earth's Past Mass Extinctions

by Peter Brannen

But the carbon cycle is not the only earth system getting short-circuited thanks to human ingenuity. We’re also living through the largest disruption to the earth’s nitrogen cycle in 2.5 billion years. This might sound like arcane geochemistry, but the ramifications are extraordinary. Plants need nitrogen to live. It’s what Miracle-Gro is made of. Until the twentieth century, almost all biologically available nitrogen was fixed by microbes in the roots of legumes. Now humans synthesize this fertilizer from fossil fuels, fixing twice as much nitrogen as the natural world does every year. Before the twentieth century, the human population was limited in size by the number of crops it could grow, which was limited by the amount of nitrogen fertilizer available in nature from sources like manure. In 1909 the German chemist Fritz Haber invented the process of artificial nitrogen fixation and destroyed these natural limits. The subsequent explosion in agriculture is directly responsible for the existence of the billions of people alive today who would otherwise not be here, most likely including myself.