There is a lot of oxygen on Earth, but where did it come from?Today, about 21% of the air on Earth is made up of oxygen.
But our planet’s atmosphere took a long time to get to the point where it was safe to breathe.
A mix of gases that formed a thick blanket around our planet 4.6 billion years ago isn’t very different from what volcanoes produce, like methane and hydrogen sulfide.
Earth’s guts were full of volatile materials, and a steady stream of cold rocks from the inner Solar System kept giving us new things to build with.
On the other hand, larger collisions sometimes heated the surface, which made the atmosphere even hotter and kept it that way.
It was also thanks to that steady stream of minerals from the sky that there was a lot of nitrogen in the form of ammonia.
When Did Oxygen Start to Fill the Air Around Earth?
There’s still a lot we don’t know about the specifics.
For example, we don’t know for sure how much nitrogen our planet got from mineral rain in the past.
Sometime around 4.3 billion years ago, Earth’s conditions started to get better. The deluge of space rocks also started to slow down.
Geochemical reactions and possible precursors to biochemistry took place because bodies of water stayed together long enough for them to happen. This made the planet’s atmosphere thicker, mostly made up of carbon dioxide and nitrogen, which made it warmer.
There may have been a few ‘whiffs’ of oxygen coming up from volcanic activity here and there.
For a while, the planet was mostly free of oxygen for its first billion years or so.
The Great Oxidation Event was what caused so many things to break down.
Earth’s first attempts at life would have had to take the energy that held together with one set of molecules and use it to make organic materials.
At some point early in the game, maybe hundreds of millions of years after the Earth formed, a way to get energy from sunlight was found.
Though it was photosynthesis, it wasn’t the kind that left a lot of oxygen behind.
That “oxygenic” type of photosynthesis may have been around for at least 3 billion years, if not longer.
Primitive microbes got a boost from a piece of biological machinery called photosystem II. It let them combine carbon dioxide and water to make the building blocks they needed, as well as a lot of energy.
As long as the planet’s oceans were filled with oxygen, there was little chance to the atmosphere.
One possible reason for this surprising lack of oxygen is that meteorites keep sliding through the sky, leaving behind volatile gases that quickly reacted with the slightest traces of molecular oxygen.
The Great Oxidation Event took place around 2.4 billion years ago when the small amount of oxygen gas started to build up into a lot of it. This led to what’s now known as the slow buildup.
Was Oxygen a Beneficial Thing for Life on the Earth at the Time?
When there was a lot of oxygen gas, it was hard to figure out how it quickly changed the Earth’s biosphere.
Oxygen is thought to be a very reactive element.
This is true even today. We have enzymes that can help us deal with the damage that free oxygen can do to our more delicate organic molecules like DNA.
If there were no ways for early organisms to deal with oxygen, they would die off in huge numbers.
It’s possible that a considerable die-off did in fact happen.
A study of isotopes in minerals that are 2 billion years old says there was a drop in oxygen concentrations as carbon was trapped in the bodies of countless microbes suffering and dying.
Interpreting this ancient record isn’t as simple as it sounds. Other studies question the assumptions, saying that the drop in oxygen might not be caused by many people dying.
By about 600 million years ago, the concentrations of molecular oxygen in our atmosphere had finally reached about 21%.
This time in history happens to be when living things became more complicated.
It’s hard to say when it comes to how much oxygen played a role. A lot of nutrients were released from a thick layer of glaciers that scratched the surface of the Earth.
On the other hand, oxygen is a very important way to get a lot of energy out of hydrocarbons today.
This is just what it needs for the modern multicellular organism on the move!
On the other hand, the exact order of oxygenation and the first complex organisms isn’t agreed upon, making the relationship a little more complicated.
Is There a Chance that Earth Will Run out of Oxygen at Some Point?
As long as the Sun is shining, plants are blooming, and photosynthesis is going on, it looks like our planet will always have a fair amount of oxygen in the air.
But that balance isn’t going to last.
The Sun’s radiation will be strong enough to break apart CO2 in about a billion years.
Without the gas, photosynthesis will come to a halt, and oxygen levels will fall to amounts that haven’t been seen in very a long time.
