What is the Oxygen Holocaust and how did we survive it?

  • The Oxygen Holocaust (otherwise known as the Great Oxidation Event) was a worldwide pollution crisis that occurred nearly 2 billion years ago
  • Before this, there was very little oxygen and high levels of methane in the earth’s atmosphere
  • The original biosphere would have been as different to us now as an alien planet
  • Then something incredible happened. Some bacteria, called cyanobacteria, learned how to directly harness the power of the sun
  • Colonies of cyanobacteria could photosynthesize more efficiently since they were operating together. These colonies flourished all over the shallow seas of the early Earth
  • They photosynthesized faster than oxygen could be bound by elements like iron. Instead, oxygen gas built up at higher and higher percentages in the atmosphere
  • Geological, isotopic and chemical evidence suggests that oxygen accumulated in the atmosphere and transformed it to an oxidizing atmosphere
  • This is why it’s known as the Great Oxidation Event
  • This was ultimately caused by the cyanobacteria producing the oxygen, which enabled the subsequent development of multicellular forms

In the article below, we tell the story of the Oxygen Holocaust, otherwise known as the Great Oxidation Event. 

This article was first published in Tribe, our digital magazine. It’s a better reading experience and doesn’t have ads. You can download it for free on iPhone and Android.

Oxygen: The apocalypse we survived

Hold your breath.

Can you make it 30 seconds? 1 minute?

Soon after you stop breathing, your brain sends out red alerts as the build-up of carbon dioxide in your body becomes dangerous.

Your mind screams “get rid of it!”

Whoosh! You exhale the exhaust and suck in oxygen.

For animals, oxygen is life-giving. It is absolutely critical for our survival.

Our blood takes in oxygen and transports it around the body, using it to carry out vital life processes in every cell. Without oxygen, our brains begin to die in mere minutes.

It’s crazy, then, to imagine oxygen as anything but a life-bringer. But billions of years ago, oxygen was a poison that threatened to destroy all of life on Earth.

Crazy, isn’t it?

You see, when life first started out, the Earth was radically different than what we are used to.

No oxygen gas. High levels of methane. The skies would have been an eerie hue of purple. Life back then was confined to small cells that gained their energy from very inefficient fermentation pathways.

It was simple, inefficient, and tiny. But then something happened.

How it happened, we aren’t certain.

Some bacteria, called cyanobacteria, learned how to directly harness the power of the sun. They combined sunlight, water, and carbon dioxide to create a vastly more efficient energy cycle.

What did it produce as a result?

Now, at first, this wasn’t a big deal. There weren’t a lot of bacteria cranking out oxygen, so the oxygen could bind with iron to make iron oxide (which we know as rust). This kept the oxygen out of the atmosphere, protecting life.

But then something radical happened.

Colonies of cyanobacteria started forming. These colonies could photosynthesize more efficiently since they were operating together. These colonies flourished all over the shallow seas of the early Earth.

Their success came at a cost. They photosynthesized faster than oxygen could be bound by elements like iron. Instead, oxygen gas built up at higher and higher percentages in the atmosphere.

To this early life, oxygen was toxic. And that’s not surprising.

Oxygen is a very reactive gas. In higher percentages, it can actually be dangerous to us as well.

Breathing 100% oxygen can damage our lungs and cause seizures. It’s a serious element.

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Source: DepositPhotos

Though we understand this nascent life did not have the ability to form complex thought, I want you to imagine what it must have been like as an invisible toxin amassed around you.

Your growth has slowed. Your friends are starving, and being attacked — being killed — by something that you can’t see.

I know we can relate to this.

The easy analogue might be COVID-19, right?

There’s an invisible toxin (in this case, a virus) that we’re breathing in, harming us and killing us.

But I want to step away from the simple analogue and go one step further.

Let’s put ourselves in the place of these cyanobacteria colonies.

You’re using this seemingly endless source of energy to power yourself, but in the process, you’re poisoning your environment. You’re changing your climate, your ecosystem, and Earth itself.

I’m sure you understand the analogue.

Climate change.

Like today, the climate change of billions of years ago (called The Great Oxidation Event) threatened to destroy all of life.

For many early bacteria, the oxygen itself simply poisoned life until it died.

For the lucky few that were able to hide themselves deep in the anoxic waters and muds of early Earth, more dangers would still lurk on the horizon.

Oxygen rose up into the atmosphere, going from a trace element to nearly 30% of the air available. This new oxygen would react with the methane in gigantic flames, converting it into carbon dioxide.

Methane, which at the time was the most prevalent gas in our atmosphere, suddenly disappeared — with carbon dioxide taking its place.

Today, we hear that carbon dioxide is a dangerous gas. Too much of it traps heat in our atmosphere, causing global warming and unpredictable climate change.

That is still true. But methane is also a greenhouse gas. And it is a much stronger insulator than carbon dioxide.

So, in the case of life billions of years ago, they actually lost their biggest greenhouse gas, meaning that too much heat started to escape the Earth.

In turn, this led to one of the greatest, most catastrophic ice ages our planet has ever seen: the Huronian Glaciation.

The Huronian Glaciation lasted 300-400 million years. That’s nearly a 10th of the Earth’s lifetime.

During that time, ice stretched down far below the polar ice caps, trapping a tremendous amount of the world’s land under unimaginable amounts of ice.

The cyanobacteria colonies, which had benefited so much from the free carbon dioxide and limitless sunlight, were now being hemmed in by ice and by oxygen — a combination that threatened to extinguish all of life.

But life wasn’t extinguished, right?

After all, we’re here. You’re reading this essay. Somehow, as Jeff Goldblum put it, “life finds a way.”

What happened? How did life find a way?

The jury is still out on the specifics, but it is believed that two events happened.

First, increased volcanic activity coupled with a decrease in precipitation (because all the water was holed up in ice) caused the Glaciation to finally end.

Second, the organisms that survived this apocalyptic 300 million years emerged much tougher and fit.

One of these tougher organisms, a tiny bacteria, had evolved a remarkable adaptation. It wasn’t able to harness light like the cyanobacteria. And it wasn’t bound by the exceedingly inefficient fermentation reactions like its predecessors. Instead, it was somehow able to harness the power of this reactive, toxic element.

It took in oxygen. And it expelled carbon dioxide and water.

This, over 2.5 billion years ago, marks the first instance of “aerobic” metabolism — meaning an organization used oxygen to carry out the basic functions of life.

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Source: DepositPhotos

This was a watershed moment in Earth’s history.

Now, the oxygen levels on Earth could be managed. Oxygen and carbon dioxide could be balanced out between the aerobic bacteria and the cyanobacteria. The efficiency of these aerobic bacteria eventually proved the basis for multicellular animal life.

Larger bacteria somehow enveloped these smaller, aerobic bacteria without ingesting them. These smaller bacteria existed inside of the larger cells in a state of symbiosis, providing the otherwise anaerobic larger cell with the ability to capture oxygen.

All animals, to this day, still keep this arrangement.

Those smaller bacteria are now called “mitochondria” and exist within every cell in our bodies. These mitochondria are the only parts of our cells that can actually process oxygen.

Mitochondria take glucose and oxygen and create carbon dioxide and water. This chemical reaction creates energy that the cell stores in a molecule called ATP that can be used throughout the cell.

I know that sounds pretty “sciency,” and I know that most of us just remember “mitochondria are the powerhouse of the cell,” but what it really boils down to is the mitochondria is what converts oxygen into useable energy for your whole body. And only your mitochondria can do that.

When we think of breathing, when we think of oxygen, we typically imagine oxygen rushing into our lungs … and then everything past that gets a little funky.

Maybe we remember that the lungs oxygenate blood.

We definitely remember the heart pumps that blood around our body. But past that, be honest, do you really think about how that oxygen gets into anywhere else? Or, more to the point, what that oxygen does?

We don’t. We just know we need it. We just know that oxygen is life-giving. Life-sustaining.

But when you break it down and examine that each molecule of oxygen has to get scooted around to every cell in your body so mitochondria can use it to turn sugar into energy — you realize that your entire state of being rests upon these tiny organelles called mitochondria that somehow didn’t get digested when a bigger cell swallowed them up.

Your existence, my existence, it’s all thanks to a tiny cell that was able to take advantage of a toxic environment.

This tiny cell was then gobbled up by a bigger cell, and the two of them entered into a union. The bigger cell protected the smaller, and the smaller provided it energy. This is the basis of all of our animal life.

A tiny aerobic cell that figured out how to harness oxygen.

And it’s thanks to this small, aerobic cell that the atmosphere of the Earth was able to be balanced.

Life exploded and the climate stabilized. It might be the greatest moment of crisis management in Earth’s history.

This brings me back to today.

We find ourselves on the precipice of a climate disaster, not unlike the Great Oxygenation Event which drove much of life to extinction.

Each year, we emit over 50 billion tons of carbon dioxide and methane, which trap extra heat in our atmosphere. This extra heat sets off cascading and chaotic climate effects from rising sea levels to brutal heat waves to desertification to violent tropical storms.

Just as the oxygen-producing cyanobacteria of billions of years ago, we are remaking the world through our waste.

The question is, will we survive Earth’s new image?

Like Jeff Goldblum said earlier, “life finds a way.”

Looking at the history of Earth as a guide, I have no doubt that if we leave life and ourselves to our own devices, life will arise that will thrive in this new environment.

It will just happen that perhaps 90% of existing species may die off in the process.

In the past, whether it be the Great Oxidation Event, Huron Glaciation, or the meteor that ended the dinosaurs; species that couldn’t compete died out. And that was most life.

Yes, these watershed events provided opportunities for new life to rise to the occasion and recreate the world through their power, but it was at the expense of nearly all other species dying out.

We are in the midst of a crisis akin to the Great Oxidation Event. But unlike the primitive lifeforms 4 billion years ago, we are sentient beings.

We think, we understand.

We plan.

We see how our actions have consequences, and we can choose to change our actions to create different consequences.

We have a choice then. We can choose to be the next generation of mitochondria.

Hold your breath. Can you make it 30 seconds? 1 minute?

Your mind is screaming for release, right?

It’s because of the build-up of carbon dioxide. This panic we feel at the build-up of carbon dioxide (a poison to us) must have been the same panic that those anaerobic bacteria felt when toxic oxygen started streaming in.

But we have the ability to do something about this.

While reducing emissions and eventually becoming carbon neutral are great, critical goals to avert a climate crisis, there is another goal we should pursue.

Reversing the damage we have already inflicted.

Luckily, through our own ingenuity, we are happening upon solutions. We don’t have to wait for the next mitochondria to evolve; we can be our own saviors.

There’s already an amazing initiative called 1 trillion trees, aiming to (you guessed it) plant 1 trillion trees to suck carbon dioxide out of the air.

This won’t be enough, but this crude form of carbon capture (drawing CO2 out of the air), may serve as a springboard to create and implement efficient and Earth-saving technologies to recalibrate our atmosphere, just as the aerobic bacteria did billions of years ago.

For billions of years, plants and animals existed in a symbiosis of breath and photosynthesis. Plants produced oxygen. Animals took that oxygen and their mitochondria returned it as carbon dioxide.

Now, we animals have upset that equation.

We have, through our industrialization, “breathed” far more out than plant life could balance.

We have become the potential horsemen of the impending apocalypse, as those cyanobacteria billions of years before us.

The question is, will we let ourselves be buried?

Or will we rise through our ingenuity to evolve, like those aerobic bacteria, to rebalance the world — ensuring our breath in equals one breath out?

Nathan Dennis

Nathan Dennis

Nathan Dennis is a Manhattan based playwright and poet of Floridian extraction. A graduate of NYU Tisch Department of Dramatic Writing, he served as a Rita and Burton Goldberg Fellow, and was awarded Outstanding Writing for the Stage in Spring of 2015. His most recent play, Lord of Florida, was workshopped by PrismHouse Theatre Company in the Fall of 2017.

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