It has been suggested MTB evolved in the early Archean Eon, as the increase in atmospheric oxygen meant that there was an evolutionary advantage for organisms to have magnetic navigation.[18] Magnetosomes first evolved as a defense mechanism in response to the increase of reactive oxygen species (ROS) that resulted from The Great Oxygenation Event.[19] Organisms began to store iron in some form, and this intracellular iron was later adapted to form magnetosomes for magnetotaxis.