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.