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Fifty percent of the nitrogen molecules in human tissues originates in an industrial machine.

They form our DNA, our amino acids, and countless other molecules essential to life.

In the 21st Century, our technology helps to create us.

This same machine could be said to have created the modern world too, as it’s nitrogen-based molecules let our population explode from 1.6 to 7.6 billion people in under 100 years.

It is called the ‘Haber process’ (link to Wikipedia) and first glance it seems like a bit of a contradiction.

Nitrogen is a colourless, tasteless, odourless gas. Our species might have evolved not to see or smell it because it makes up an overwhelming 78% of the air around us.

We inhale it in every breath, alongside oxygen (which makes up 21%).

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 to create amino acids, proteins, DNA, and tons of other important things.

Plants in particular have an insatiable need for nitrogen and struggle to get it, even though we are all surrounded by it.

Just like a sailor dying of thirst while stranded in the middle of the ocean, life on Earth is surrounded by nitrogen it can’t use.

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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 than to make 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.

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 348,228 of them 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.

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

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.

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During this period, life was basic. Only tiny single-celled organisms could live with so little ‘severed’ nitrogen available.

After millions of years, some types of bacteria evolved to produce chemicals that broke down nitrogen in the air in a more subdued way.

Some kinds of these bacteria eventually evolved a partnership with many plant species, who grew nodules in their root systems just to house their colonies.

With this relationship, plants 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

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 ‘bioavailable’.

With this partnership, plants and animals seem to have sorted out the nitrogen issue.

Life blossomed from tiny single cells to complete ecosystems.

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But there was another problem.

Every time 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.

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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, considering how fast many plants grow in the spring.

But this isn’t 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.

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

Enter one of the most important people in the history of our species. Fritz Haber.

Just before WWI, Haber discovered that you can break nitrogen’s triple bond by 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.

Even better, the process was both economic and scalable.

This was the ‘Haber process’, and it’s one of the most important discoveries in our history.

With ammonia in their fertiliser, our crops 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.

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 grew from 1.6 billion to 7.6 billion (as of writing), and it continues to grow.

We are all the product of the industrial production of food and fertiliser. About 50% of the nitrogen found in human cells originated from the Haber process.

Nitrogen-fixed fertiliser

The Epilogue

The story doesn’t quite end there. Such a dramatic development has naturally brought some side effects.

Plants only end up absorbing about 50% of the ammonia in the fertiliser we give them. When it rains, the rest is washed away from agricultural and residential areas into downstream 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 only until the excess of nitrogen washes away.

When the algae dies, the huge volume 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.

If you have any questions about this article, please submit them to our open Ask Me Anything.

The challenge that we face in the 21st Century is in finding ways to manage the unintentional outputs of our global civilisation, like our incredibly valuable nitrogen.

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Ben McCarthy

Ben McCarthy

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