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TL;DR: Nitrogen is one of life’s most precious resources. Discovering how to industrially produce it (as ammonia) let our population break free of natural limits, and explode.

An amazing fifty percent of the nitrogen atoms now found in human tissues originated inside an industrial machine invented relatively recently. These molecules form our DNA, our amino acids, and countless other things essential to life. But how did this bizarre situation come about?

The Haber process

In the 21st Century, our technology has helped to create us. But this same industrial machine could be said to have created the modern world too, as its development let our population skyrocket from 1.6 to 7.6 billion people in under 100 years, by producing enough fertiliser to grow the food needed to sustain all that extra life.

The machine is called the β€˜Haber process’ and at first glance it seems like a bit of a contradiction.

Nitrogen is everywhere, but we can’t use most of it

Nitrogen is a colourless, tasteless, odourless gas. Human beings cannotΒ  see it or smell it, and our species might have evolved that way because it makes up an overwhelming 78% of the air around us.

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We inhale nitrogen in every breath alongside oxygen (which makes up 21% of our air). But unlike oxygen, we exhale nitrogen straight back out again.

The contradiction is that every cell in our bodies (and every cell of every living creature) desperately needs nitrogen. Plants in particular have an insatiable need and struggle to get it, even though we are all surrounded by it. Just like someone dying of thirst while stranded in the middle of the ocean, life on Earth is surrounded by nitrogen it can’t use.

Life on Earth is a bit like Tom Hanks in Castaway (2000)

Nitrogen’s triple bond

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.

The problem is that most nitrogen atoms are tightly bonded with other nitrogen atoms using three of its seven electrons, creating what is known in chemistry as a powerful triple bond (N≑N).

As I was writing this page, I had to do a bit of a refresher on High School chemistry. I had a cranky old teacher who preferred talking about his sailing adventures from 40 years ago rather than making chemistry interesting. It was not my best subject!

Concepts like a triple bond in a colourless, odourless gas are pretty abstract. It’s part of what makes some sciences like chemistry difficult for us. When we can’t directly touch, hear, see, or smell something, it’s difficult to build the mental frameworks needed to understand it.

A well-kept secret

I found out that it took until 1772 for human beings to discover the existence of nitrogen in the first place.

Let’s unpack that.

Our species has existed for 350,000 years, and it took us almost our entire existence thus far to discover a gas that we inhale with every breath. At the end of the day we’re a species that evolved to hunt, gossip, invent things, tell stories, and have sex. But when we finally did work out the concept of nitrogen (and it’s triple bond) we conquered the Earth.

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Severing the triple bond

Chemically speaking, triple bond is formidable. Almost no cell can break it to re-use the nitrogen for other things, and that’s why we always exhale it. For it to be used by life, the bond must be severed.

Very early in Earth’s history, the only way to do this was pure chance. When the bolts of a lightning storm seared through the air, sometimes the nitrogen molecules in the air would be cleaved in two. During this period, life was basic. Only tiny organisms could live with so little β€˜severed’ nitrogen available.

A bolt of lightning seen in slow motion

After millions of years, some bacteria evolved to produce chemicals that broke down nitrogen in the air in a more subdued way. They eventually evolved a partnership with many plant species, who grew nodules in their root systems specifically to house their colonies.

With this relationship, plants on land could slowly but regularly draw nitrogen from the air and soil and convert it into a usable form. Animals that ate the plants would inherit these compounds and use them.

If you pull many plants out by their roots, you’ll see the bulbs that house nitrogen-fixing bacteria

Nitrogen compounds helped life on Earth to flourish and evolve

This is a little technical but when the bond is broken, nitrogen forms compounds like ammonium (NH4), ammonia (NH3), nitrite (NO2), and nitrate (NO3). These compounds are usable for life, which is known as being β€˜bioavailable’. With this partnership, plants and animals seem to have sorted out the nitrogen issue. Life blossomed from tiny single cells to complete ecosystems, like jungles, swamps, grasslands, and forests.

But there was another problem.

When it rains, plants and animals receive the water they need to survive. But for what it gives, it also takes something away. All of these bioavailable nitrogen compounds dissolve super easily in water, so every time it rains the hard work of the bacteria gets washed away.

Almost every ecosystem on land is still limited by a bottleneck of nitrogen, and does not grow as fast as it could. This may be surprising to some gardeners, but almost all wild plants don’t grow to their full potential.

Under perfect conditions, including a plentiful supply of nitrogen, some species of bamboo can grow up to 91 cm (36 inches) per day.

Fritz Haber’s world-altering invention

But most importantly for us human beings, nitrogen’s triple bond restricts the growth of our plants. Our crops.

Enter one of the most important (but unrecognised) people in the history of our species. Fritz Haber.

Just before WWI, Haber discovered that you can break nitrogen’s triple bond by mixing it with natural gas and passing it across several catalysts (chemicals that speed up reactions) while under pressure. You end up with lots of ammonia, which is mixed in with plant fertiliser. The process was both economic and scalable.

This was the β€˜Haber process’, and it’s one of the most important discoveries in our history. With ammonia in their fertiliser, our crops grew like crazy, as explained in 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.

Emphasis on that last part. It’s not an exaggeration to say that this discovery created the modern world as we know it.

The Haber process has been called the β€œdetonator of the population explosion.” The number of people on Earth is now 7.6 billion (as of writing), and it continues to grow. If you weigh the biomass of all the mammals on the Earth, 96% of it comes from us and our livestock.

We are all the product of the industrial production of food and fertiliser.Β This is why fifty percent of the nitrogen found in human cells was processed in a machine.

Nitrogen-fixed fertiliser

But the story doesn’t end there

Such a dramatic development has naturally brought side effects.

Plants only absorb a portion of the ammonia in the fertiliser we give them. As always, when it rains the rest is washed from agricultural and residential areas into rivers, and eventually into the ocean.

The unintentional introduction of so much nitrogen in these environments creates problems, usually as an enormous bloom of algae (tiny waterborne plants). The bloom survives until the excess of nitrogen washes away. When it dies, the huge volume of decaying matter absorbs all of the oxygen in the surrounding water. It makes the water unbreathable for every fish or animal that cannot escape the area.

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

A green 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.

Back to that contradiction

The challenge of scarcity faced by life throughout most of its history has been replaced by a challenge posed by abundance.

In the 21st Century, we are challenged to find ways to manage the unintentional outputs of our global civilisation like our nitrogen, without giving up its incredible advantages.

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Ben McCarthy

Ben McCarthy

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