Evolution upset: Oxygen-making microbes came last, not first Get ready to rewrite those biology textbooks - again. Although the "lowly" blue-green algae, or Cyanobacteria, have long been credited as one of Earth's earliest life forms and the source of the oxygen in the early Earth's atmosphere, they might be neither. By creating a new genetic family tree of the world's most primitive bacteria and comparing it to the geochemistry of ancient iron and sulfur deposits, Carrine Blank of Washington University has found evidence that instead of Cyanobacteria being very ancient, they may have appeared much later, perhaps as much...