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

An incredible fifty percent of the nitrogen atoms in the tissue of any person alive today have originated inside of an industrial machine.

These atoms help form our DNA, our amino acids, and countless other molecules essential to life. But how did this situation come about?

The Haber process

In the 21st Century, our technology is like a life support system for our civilisation. Nowhere is this phenomenon so clear as with our agriculture, where the development of a particular type of machine let our population boom from 1.6 to 7.7 billion people in under 100 years.

The machine uses what is called the ‘Haber process’ and at first glance it seems like a contradiction.

Nitrogen is a colourless, tasteless, odourless gas. Human beings cannot see it or smell it, even though it makes up an overwhelming 78% of the air around us.

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 the cells of every living creature) desperately needs nitrogen. Plants in particular have an insatiable need and struggle to get 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)
Life on Earth is a bit like Tom Hanks in Castaway (2000)

Nitrogen’s triple bond

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

Concepts like a triple bond in a colourless, odourless gas are pretty abstract. When we can’t directly touch, hear, see, or smell something, it’s difficult to build the mental frameworks needed to understand it.

What’s more, 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. But when we finally did work out the concept of nitrogen (and it’s triple bond) we conquered the Earth.

Severing the triple bond

Chemically speaking, a triple bond is formidable. Very few forms of life can break it to use the nitrogen for their essential molecules, and that’s why we exhale it.

Very early in Earth’s history, the only way to sever the bond 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 ‘severed’ nitrogen available.

A bolt of lightning seen in slow motion. Get more nature content like this on the
A bolt of lightning seen in slow motion. Get more nature content like this on the Discover Earth app.

After millions of years, some species of bacteria evolved to produce chemicals that broke down nitrogen in a more subdued way. They eventually evolved a partnership with many plant species, who grew nodules in their root systems specifically to house these bacterial 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
If you pull many plants out by their roots, you’ll see the bulbs that house ‘nitrogen-fixing’ bacteria

Life begins to flourish

When the triple bond is broken, nitrogen reforms into molecules 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 and spread to new environments across the Earth.

But there was another problem.

When it rains, plants and animals receive the water they need to survive. But 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. It may be surprising to gardeners, but almost no wild plants (or weeds) grow to their full potential.

For example, under perfect conditions including a plentiful supply of nitrogen, some species of bamboo can grow 91 cm (36 inches) per day.

Enter Fritz Haber

Most importantly for us human beings, nitrogen’s triple bond restricts the growth of our crops.

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

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 is both economic and scalable.

Incidentally Haber also discovered how to make chlorine gas – just in time for WWI. This may be why he isn’t more well known.

His method was called 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, 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 “detonator of the population explosion.” The number of people on Earth is now 7.7 billion (as of writing), and it continues to grow. We’re still in the explosion.

We exist because of the industrial production of food and fertiliser, and this is why every cell in our body contains nitrogen once processed in a machine.

Nitrogen-fixed fertiliser
Nitrogen-fixed fertiliser

Flow-on effects

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 (microscopic plants in the water). The bloom survives until the excess of nitrogen washes away which it inevitably does. When it dies, the huge volume of decaying plant matter absorbs all of the oxygen in the surrounding water, making it unbreathable for every fish or animal that cannot escape.

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

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

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, our challenge is to find ways to manage the unintentional outputs of our global civilisation like our abundance of nitrogen, without giving up its incredible advantages.