Attributing life‐or‐death importance to organisms too small to be seen without great magnification is difficult, but consider that the prokaryotes: Decompose complex organic molecules and return to the soil and air the elements needed for growth of all organisms. Participate in complex biogeochemical webs that concentrate minerals—iron, manganese, copper, and others. Maintain soil fertility by fixing atmospheric nitrogen, thus assuring the supply of available nitrogen for protein and nucleic acid synthesis by all organisms. Are the base of food webs on land and in the oceans. Are crucial links in the sulfur, phosphorus, carbon, oxygen, and nitrogen cycles. Using novel metabolic pathways, both discharge into the atmosphere and extract from it all of the major reactive gases: nitrogen, oxygen, carbon dioxide, carbon monoxide, sulfur-containing gases, hydrogen, methane, and ammonia.