The benefits of community life impress microbes early on. One microbe's waste is another's lunch. Eating, reproducing and making waste are consistent features in the continual development of life. Microbial mats form richly layered ecosystems and, under the right conditions, these become stromatolite bacterial skyscrapers.
The blue-greens live in the top layers, slipping in and out of UV-lightshielding sheaths to gather solar energy. Cyanobacteria produce prodigious amounts of food. "Consumer" bacteria, immune to oxygen, quickly join the cyanobacteria. Beneath them live mixed populations of consumers and producers, each possessing unique diets, tolerances for oxygen, light and sulfides.