Major atmospheric changes radically transform Earth's surface. "Red Beds," those huge, rusty piles of uniformly oxidized iron mineral, form everywhere on the planet. BIFs stop accumulating.
The lucky among the anaerobic bacteria find mud flats and airless niches in which to survive. These relics of the Archean atmosphere still thrive in the 20th century – at the sulfurous smelling edges of the sea, in swamps, inside insects and inside us.
In oxygen-tolerant and now, oxygen-loving bacteria, grand innovations continue. Their mode of respiration is about to lead to new life forms emerging from a dramatic symbiogenesis.