Before all the cyanobacteria turned up, earth had a nice inert atmosphere. They start with their newfangled photosynthesis and suddenly the atmosphere is full of this horribly reactive oxygen stuff. Now the planet is crawling with life, irreparably damaging the unspoilt beauty of our natural geology. You can hardly find a piece of rock on the planet that doesn't have algae or lichen all over it. Cyanobacteria ruined this planet for their own selfish ends.