The First Poisoning

For most of life's time on Earth, the air you breathe now was poison. Then something small and green learned a new trick — it ate sunlight and breathed out the poison, slowly, for a hundred million years. The oceans turned the colour of rust, the poison crept into the sky, and almost everything alive suffocated. It was the worst thing that ever happened to life. And the reason you survived it is a secret still folded inside every breath you take.