For more than half the life of the planet, there was more carbon dioxide than oxygen. Some oxygen might have been produced by solar radiation breaking down atmospheric water vapour, the lighter hydrogen escaping into space; but what eventually displaced CO2 from its dominant position, around 2 billion years ago, is thought to have been the photosynthetic efforts of blue-green bacteria to build carbohydrates from water and carbon dioxide. Unaware that it was one of the main culprits, one of these early organisms describes its view of oxygen as a major pollutant . . .
“Our environment’s doomed,” cried a microbe of old,
“If we don’t get to grips with pollution.
It’s getting much worse now, or so I’ve been told;
We really must find a solution.
“We’re worried that soon there won’t be enough
CO2, so we can’t photosynthesise.
Some say we’re to blame for this oxygen stuff,
But how can that be? It’s just wicked lies . . .
“The Sun is the culprit: its harsh UV light
Is breaking apart H2O
Into H2 and O2. The H2 takes flight,
Leaving O2 behind, as we know.
“If nothing is done, we are doomed to expire.
This poisonous air must be banned.
It’s far too reactive: it makes things catch fire,
And spreads rust and rot through the land.
“Who knows what effects all this noxious gas
Will have on our future? It’s scary:
Could mutants arise, of incredible mass,
Big brains, arms and legs, and quite hairy?”