Roughly half of the nitrogen atoms inside the protein in a human body alive in 2026 did not come from soil bacteria, lightning, or any of the slow biological cycles that fed every generation before the twentieth century. They came out of a steel reactor, pulled from ordinary air by a chemical reaction first run successfully in a laboratory in Karlsruhe, Germany, in 1909. The chemist was Fritz Haber. The reaction now feeds about four billion people.
That figure, half the nitrogen in the average human body, is one of the strangest statistics in modern biology. The amino acids that build muscle, the bases that spell out DNA, the enzymes that keep a heart beating — for billions of people, a coin flip decides whether any given nitrogen atom inside them was fixed by a microbe or by a factory.
The bond that almost nothing could break
Nitrogen gas makes up about 78% of the atmosphere. Every breath floods the lungs with it. And almost none of it is useful. The two nitrogen atoms in N₂ are locked together by a triple bond, one of the strongest covalent bonds in chemistry, and plants cannot pry them apart. Crops need nitrogen in a reactive form — ammonia, nitrate, or amino acids — to build proteins and chlorophyll.
For most of the 10,000 years of farming, that reactive nitrogen came from a thin trickle of natural sources: lightning strikes, which crack N₂ in the atmosphere; soil bacteria living in the roots of legumes like clover and beans; and the patient recycling of manure, compost, and human waste. As Mother Jones has documented, farmers without the chemistry vocabulary still understood the pattern: rotate the field, spread the dung, or watch the yield collapse.
By the late nineteenth century, European agriculture was running out of cheating room. Cities were swelling, rural labour was thinning, and the imported guano deposits off the coast of Peru — mountains of seabird droppings rich in nitrate — were being shoveled into ships as fast as workers could load them. The chemists understood the problem clearly. The air above every wheat field contained, in principle, enough nitrogen to feed it forever. The triple bond just had to be broken.
What Haber actually did
Fritz Haber’s solution, demonstrated in a tabletop apparatus in his Karlsruhe laboratory, was brutal. He passed nitrogen and hydrogen gas over a catalyst at high temperature and pressure — conditions closer to the inside of a torpedo than a chemistry beaker. The reaction yielded liquid ammonia, drop by drop, from thin air.
BASF bought the patent. A young engineer named Carl Bosch then spent five years working out how to scale the reaction from a bench-top demonstration to an industrial plant capable of holding hundreds of atmospheres of pressure without exploding. The first commercial Haber-Bosch facility opened at Oppau in the early 1910s. Chemical & Engineering News has traced how that single industrial process became the backbone of the modern food system, with synthetic fertiliser now spread on fields from Iowa to the Punjab.
The chemistry has barely changed in a century. Modern ammonia plants still run a recognisable version of Haber’s reaction, only with iron catalysts and more efficient heat recovery. Ammonia from these reactors now sustains the global food system, the great majority of it destined for fields.
Counting atoms in a human body
The claim that half the nitrogen in your body was fixed in a factory sounds rhetorical. It is closer to a budget. Global flows of reactive nitrogen have been tracked: how much enters the biosphere each year from biological fixation, lightning, and Haber-Bosch; how much of that nitrogen ends up in crops; how much of those crops are eaten by humans directly or pass through livestock first; and how the resulting nitrogen distributes itself across the protein in 8 billion bodies.
The arithmetic delivers a striking result. In 1900, essentially zero percent of the nitrogen in human tissue had passed through an industrial reactor. By the early 21st century, the figure was roughly half. Chemistry World’s overview of nitrogen fixation puts the same point another way: without synthetic ammonia, roughly half the people now eating breakfast would never have existed, because the soil could not have supported the calories that fed their parents and grandparents.
The provenance is not evenly spread across the body. Nitrogen is concentrated in protein — muscle, collagen, enzymes — and in the nucleotides of DNA and RNA. Each amino acid molecule carries at least one nitrogen atom in its backbone. The same is true for every base pair in the genome. When a child grows three centimetres in a summer, the nitrogen atoms knitting together that new tissue were, statistically, as likely to have come from a steel pressure vessel as from any natural source.
The two men, and the darker ledger
Haber received the Nobel Prize in Chemistry for the ammonia synthesis. By then he had also overseen the first large-scale use of chlorine gas as a weapon, at Ypres in April 1915, where German cylinders released chlorine across French and Algerian lines. His wife Clara Immerwahr, herself a chemist, died by suicide days after he returned from supervising the attack. Haber went back to the eastern front to direct further gas operations within weeks.
Bosch received the Nobel Prize for high-pressure chemistry. Discover Magazine, reviewing Thomas Hager’s history of the invention, describes the same plants that fed Europe being converted during the First World War to make nitrates for explosives, prolonging a conflict that the Allied naval blockade of Chilean nitrate imports should have ended within months. The munitions output of Oppau and the later plant at Leuna kept German artillery firing for three more years.
The ledger gets darker. Haber’s institute developed cyanide-based pesticides in the 1920s. A derivative, Zyklon B, was later used by the Nazi regime to murder more than a million people in extermination camps — including members of Haber’s own extended family. Haber himself, a converted Jew, had been forced out of Germany and died in exile in Basel.
The chemistry that built half the protein in every living human came from the same laboratory, the same career, the same mind.
A factory hooked to a gas pipeline
The modern Haber-Bosch process eats energy. To produce the hydrogen feedstock, plants strip it from natural gas in a step called steam methane reforming. The reaction itself runs at high temperature and pressure, conditions that demand sustained high-pressure steam. A recent Hackaday piece on a hobbyist building a miniature Ostwald reactor — the second-stage process that turns ammonia into nitric acid — captures how the industrial chain still mirrors the architecture Bosch laid down in the early twentieth century: fix nitrogen, oxidise it, sell it.
Ammonia production now consumes a significant fraction of global energy and is responsible for substantial CO₂ emissions. The world’s food supply, in other words, rides on a pipeline of natural gas. When that pipeline shakes — when Russian gas exports collapse, when shipping routes near the Strait of Hormuz get disrupted, when European fertiliser plants idle because the cost of methane outpaces the market price of ammonia — the price of bread follows within a season.
The enzyme the bacteria use instead
Plants cannot do what Haber did. But bacteria can, at room temperature, using a metalloenzyme called nitrogenase. The enzyme contains a cluster of iron, sulfur, and molybdenum atoms that somehow grips an N₂ molecule and feeds electrons into it until the triple bond breaks. It uses a remarkable amount of cellular energy — the enzyme burns sixteen ATP molecules to fix a single N₂ into two molecules of ammonia — but it does the job at ambient pressure, with no steel vessel required.
For decades, working out exactly how nitrogenase performs that trick was considered one of the hardest problems in computational chemistry. Researchers have recently made progress in decoding the enzyme’s electronic structure, work that matters because if engineers can copy the chemistry of nitrogenase, they could in principle build ammonia plants that run on sunlight and air, with no steam reformer in the loop.
That work sits inside a wider hope: that the next century of nitrogen fixation might unhook the global food supply from fossil methane. It has not happened yet. The factories still hum on natural gas.
What a half-factory body actually means
If you eat bread, meat, eggs, or dairy from any industrial supply chain, the nitrogen ratio in your tissue is roughly the same as the global average. Vegetarians who source food from organic, legume-rich rotations carry a slightly lower industrial fraction. People in subsistence farming systems, who rely on manure and cover crops, carry less still. But almost nobody on Earth is below 20%. The reaction has saturated the food system.
That fact has consequences beyond biography. Reactive nitrogen does not stay in crops. About half of every tonne of fertiliser applied to a field runs off into groundwater, evaporates as nitrous oxide — a greenhouse gas roughly 300 times more potent than CO₂ — or volatilises as ammonia. The Gulf of Mexico dead zone, the algal blooms in Lake Erie, the eutrophication of the Baltic: all of them are downstream of the same triple bond that Haber learned to break. The New Yorker recently revisited the long debate over whether plants might one day be engineered to fix their own nitrogen, sidestepping both the factories and the runoff. That research is decades old and still inching forward.
The point is not that Haber-Bosch can be undone. It cannot. Removing it tomorrow would mean a planet that could feed roughly four billion people instead of eight. The point is that a chemical reaction first run in 1909 has, in just over a century, become the largest single intervention any human technology has made in the biosphere. It is woven into the calories of every meal, the atoms of every cell, the price of every loaf of bread, and the chemistry of the rivers downstream of every cornfield.
Hold up a hand. Look at the skin, the muscle moving underneath, the bone beneath that. Roughly half the nitrogen in what you are looking at came out of a steel reactor that did not exist when your great-grandparents were born.
