Fritz Haber and Carl Bosch were two chemists who invented a way to turn air into bread, built factories the size of small cities, made enormous fortunes, helped engineer the deaths of millions of people, and saved the lives of billions more.

Their work stands, I believe, as the most important discovery ever made. See if you can think of another that ranks with it in terms of life and death importance for the largest number of people. Put simply, their discovery is keeping alive nearly half the people on earth.

Most people do not know the names of either the men or their invention. But we should thank them every time we take a bite of food. Their work lives today in the form of giant factories, usually located in remote areas, that drink rivers of water, inhale oceans of air, and burn about 2 percent of all the earth’s energy. If all the machines these men invented were shut down today, more than two billion people would starve to death.

Or think of it this way: Inside your body, every protein molecule, every cell, and every stitch of DNA includes atoms that are there because of this invention. Half of the nitrogen in your body is synthetic, the product of a Haber-Bosch factory.

I dive deeply into the history in my book, The Alchemy of Air, but the basic idea is this: 80 percent of the atmosphere around us is nitrogen, but we cannot use a single atom of it. We breathe it in and out all day long without incorporating any of it. Atmospheric nitrogen is inert, a dead molecule, because it exists in the form of two N atoms very tightly bound to each other with triple covalent bonds. In this form, the nitrogen is unavailable for use by living organisms (with the exception of a few groups of bacteria). To get into our bodies, to nourish us — and nitrogen is essential for nutrition; it is the fourth most common element in our bodies; proteins and nucleic acids depend on it — the atmospheric nitrogen must be “fixed,” the two N atoms torn apart and reforged into new molecules with other elements, mostly oxygen, carbon or hydrogen. Nitrogen fixation is a difficult, energy-intensive, and critical process.

Haber and Bosch figured out how to do it at an industrial level around 1912. The same basic process they discovered a hundred years ago is used today in scores of huge factories around the world that produce a flood of synthetic nitrogen fertilizer. That fertilizer feeds the crops that feed the animals that feed you. Thanks to Haber-Bosch factories, a bit of the almost limitless supply of natural nitrogen from the air is purified, processed, chemically altered, made into fertilizer, and eventually ends up on your plate. That’s why half the nitrogen in your body is synthetic.

The work of Haber and Bosch changed the chemical industry, altered the history of Germany, and in many ways made possible the rise of Hitler. Haber-Bosch turned Malthus on his head. Haber-Bosch is the reason our grocery shelves (in the US, at least) are groaning, more people aren’t starving, and we are able to have a population explosion at the same time as an obesity epidemic.