Microbial life is heavily implicated in all the biogeochemical cycles, dwarfing the contribution of multicellular organisms—which in any case have microbes at the root of their metabolism. Mitochondria and chloroplasts, the main energy- producing organelles in animal and plant cells, both have evolutionary origins as once-free bacteria annexed into the greater whole. . . . Gaia’s metabolism is microbial. WILLIAMS AND LENTON
