Oxygen
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Oxygen

Twenty-one percent of the air that you’re breathing right now is oxygen. Like most elements it’s the remnant of a supernova explosion, one of the most incredible phenomena in the universe.

Oxygen is one of the most reactive and destructive elements, and when it first started to build up in the Earth’s atmosphere 2.4 billion years ago it almost destroyed all of life.

We are descended from the species that survived that ‘Oxygen Catastrophe’. Here’s what happened.

2.4 billion years ago all of life on Earth, including our ancestors, were tiny single-celled species similar to bacteria or algae.

Cyanobacteria. Source: Journey to the Microcosmos
Cyanobacteria. Source: Journey to the Microcosmos

These species filled the shallow oceans with life, and many of them lived by photosynthesising the Sun’s light. They broke apart water molecules and released the oxygen inside as a waste product, which gradually diffused into the atmosphere.

On land the continents were barren of life and covered in rocky outcrops. Many of these rocks contained iron, which acted as a ‘sink’ that absorbed almost all of the new oxygen as it was produced.

Rocks that contain iron will react with oxygen, creating a red glow. Many of them are still around from this ancient era.
Rocks that contain iron will react with oxygen, creating a red glow. Many of them are still around from this ancient era.

But over millions of years life grew in abundance and the rocks became fully saturated with oxygen, leaving it with nowhere else to go but to build up in the atmosphere.

This was the cause of the oxygen catastrophe which almost killed all life on the Earth before it had even really started.

Oxygen is an element that is in perpetual need of electrons. It will rip them from even highly stable molecules, leaving them as an electron-hungry ‘radical’ that will repeat oxygen’s theft elsewhere.

Once free in the atmosphere and no longer being absorbed by rocks, oxygen diffused into the ocean and began to attack all living cells by tearing apart their cell membranes. Almost all of life went extinct, victim to the toxic effect of its own waste.

Evolution saved life. A species evolved that was not just resistant to oxygen, but could harness its power and use it in its own metabolism. This species invented respiration, the process taking place within your lungs with every breath. It repopulated the oceans, and is one of our ancestors.

It kickstarted the sustainable cycle of plants creating oxygen, and animals consuming it that is still around today.

Plants releasing bubbles of oxygen into the atmosphere.
Plants releasing bubbles of oxygen into the atmosphere.

In modern times, we are accustomed to the ‘side effects’ of having a high concentration of oxygen in the atmosphere. We know that certain materials can, with just a spark, burst into flame.

Fire is oxygen acting upon a material, ripping it apart for its electrons. Things like bushfires, furnaces, and combustion engines would not be possible in a low oxygen atmosphere, and neither would complex life.

A forest in the process of being ‘oxidised’.
A forest in the process of being ‘oxidised’.

Life’s solution to the oxygen catastrophe was not to remove it from the atmosphere, but to learn how to use it.

The extra energy that life unlocked because of oxygen gave it the potential to become vastly more complex, and you utilise this ancient chemical breakthrough in every breath.