Earth life forms require energy and carbon for growth and reproduction. They satisfy these requirements through a variety of processes. Some skilled individuals produce their own food; many rely on others to make it for them.
By this time, microbes have evolved every metabolic mode known to 20th century scientists. Tiny gas-eating microbes, without using light, refine methods of making food and energy from sulfide, methane, ammonia, oxygen and carbon dioxide. Cyanobacteria and their kin, using sunlight as a source of energy create food from atmospheric carbon dioxide. Dependent on these primary producers, many microbes mix and match modes.
Stromatolite reefs, monuments of bacterial life, continue expanding across the planet.