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As soon as people learned to create nitrogen-based molecules, our population jumped from 1.6 billion people to 7 billion people. This may make nitrogen the most important chemical in the industralised world.

It came to be so important because of a few chemical properties that makes it both rare and necessary for life.

Nitrogen is the seventh most abundant element in the Milky Way, and like many elements it is formed as a residue from an exploding star. There is quite a lot of it, and something that we don’t often realise is that it’s nitrogen forms an impressive 78% of the Earth’s atmosphere. Most of the air you are breathing now is nitrogen. Only about 21% is oxygen.

But while we use oxygen in every breath, we exhale nitrogen straight back out again. This is even though every cell needs nitrogen to create amino acids, proteins, nucleic acids (like DNA), and a ton of other important things. Plants in particular have an insatiable need for nitrogen and actually struggle to get it, even though they are surrounded by it.

It turns out to be a situation like a sailor lost at sea who is running out of water. He’s surrounded by it, but cannot drink it.

The problem is that nitrogen atoms, like the free floating nitrogen in the air, usually bond with other nitrogen atoms using a powerful triple bond (N≡N). But this triple bond is formidable. Almost no cell can break it to re-use the nitrogen for other things. For it to be used by life, the bond must be broken.

Early in Earth’s history, the only way to cut this bond was pure chance. Lightning was the only way to cleave the bond in two. Much later, some forms of bacteria learned to produce chemicals that broke it down in a more subdued way. Over time, these bacteria developed a partnership with plants, who grew nodules in their root systems to house colonies of these bacteria.

With this relationship, plants could (albeit slowly) draw nitrogen from the air and soil and convert it into a usable compound. Animals that ate the plant would inherit these compounds and use them.

Many planets evolved to have bulbs in their roots that houses nitrogen-fixing bacteria

When the bond is broken, nitrogen forms compounds like ammonium (NH4), ammonia (NH3), nitrite (NO2), and nitrate (NO3). With the indigestible triple bond removed these compounds are usable for life, also known as being ‘bioavailable’.

With this partnership, plants and thus animals seem to have sorted out the nitrogen problem, though it was not a perfect fit. All of these compounds dissolve very easily in water. Each time it rained, the efforts of the hard working bacteria are washed out of soil and out into the oceans.

So while plants can get nitrogen, it is still a major bottleneck restricting plant growth and thus the growth of a whole ecosystem.

This is where one of the most influential people in history gets involved. Fritz Haber.

In the first half of the 20th Century, Haber discovered a economic means of producing vast quantities of ammonia, one of the bioavailable compounds of nitrogen. It’s called the ‘Haber process’, and it’s one of the most important and least appreciated discoveries in human history.

It works by combining nitrogen in the air with hydrogen from natural gas. They are put together in a chamber under high pressure and high temperature with a catalyst (a type of chemical that speeds up a reaction). Over 97% of the material gets converted to ammonia, which is then mixed in with fertilisers.

The Haber process was a landmark development as it led to ‘nitrogen-fixed’ fertilisers on an industrial scale. With the abundance of nitrogen in their fertiliser, plants grew like crazy. From the Wikipedia page Haber process:

The Haber process now produces 450 million tonnes of nitrogen fertilizer per year... Three to five percent of the world’s natural gas production is consumed in the Haber process (around 1–2% of the world’s annual energy supply). In combination with pesticides, these fertilizers have quadrupled the productivity of agricultural land by removing the bottleneck of bioavailable nitrogen.

Emphasis on that last part. It’s not an exaggeration to say that this discovery created the modern world as we know it. By removing this bottleneck and drastically improving our ability to grow food, the Haber process has been called the “detonator of the population explosion”. The number of people on Earth grew from 1.6 billion to 7.5 billion, and it continues to grow.

Put another way, we are all the product of the industrial production of food and fertiliser. Nearly 50% of the nitrogen found in human tissues originated from the Haber process.

Nitrogen-fixed fertiliser

But the story doesn’t end there. Such a dramatic development has brought side effects.

Plants only end up absorbing about 50% of the nitrogen compounds in the fertiliser we give them. The rest leech into the soil and run off into the ocean.

The unintentional introduction of so much nitrogen in these environments usually creates an enormous bloom of algae. The bloom is always short lived, surviving only until the excess of nitrogen washes away. When the algae dies, the huge volumes of decaying plant matter absorbs all of the oxygen in the surrounding water. This suffocates every marine animal that cannot escape the area.

These algae blooms can be so extensive that they can be seen from space.

An algae bloom in Lake Eyrie, caused by nitrogen fixed fertilisers and torrential rains. Image credit: NASA

In the picture above, the green swirling shapes in the water are algae, caused by the fertiliser run off of nearby farms. It’s a time bomb for local animals to get out or asphyxiate once it dies.

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Ben McCarthy

Ben McCarthy

Ben is the Founder of Discover Earth and the author of the Big Ideas Network.