Nature mentions a study about how early multicellular organisms
may have learnt to breathe in the air: by evolving next to certain
cyanobacteria as those found in Los Roques right now. Los Roques
is a group of Venezuelan islands at 11°51′27″N 66°45′27″W .
According to the authors, the lacoons there may represent a similar
environment to the one that existed during the Ediacaran: very low
oxygen levels but with bacteria that would produce oxygen..
The area is usually extremely salty. Almost no animal can survive
there. Still, during the day those bacteria expel oxygen as waste and
this oxygen goes just to the upper milimeter of the bacteria mats.
Insect larvae use that oxygen now. Scientists think such bacteria could
have produced a sort of oasis for primitive animals, which would
otherwise not have been able to find enough oxygen for their systems.