Herbivores eat plants, and carnivores eat animals that eat plants, to get their energy.

Plants and many bacteria create their own energy through photosynthesis, which depends on chlorophyll…which requires nitrogen.

As we’ve described in other episodes, most nitrogen on Earth is in the form of N2, the inert nitrogen gas that won’t bond with other compounds, making it useless to plants.

So, most plants rely on bacteria that cling to their roots and split the nitrogen in the soil for them. But when they can’t get enough, humans help them out, with nitrogen-rich fertilizers.

Early fertilizers relied on naturally concentrated nitrogen. For instance, bat colonies eat insects, which contain nitrogen, then excrete nitrogen-rich droppings. For centuries, humans harvested tons of bat guano to fertilize our crops.

But demand outstripped supply, so we had to invent a new source. At the start of the twentieth century, two German chemists devised a way to combine the nitrogen in air with hydrogen produced from natural gas to form ammonia, NH3. And their work won a Nobel prize…

Because liquid ammonia could then be used to mass produce nitrogen-rich fertilizers. This drove the massive expansion of industrial agriculture—which has both created and allowed us to feed a growing global population.