Cyanobacteria seems to have evolved relatively early in earth’s history. what happened to the oxygen the earliest cyanobacteria released? it allowed for more complex life forms to evolve. it reacted with iron in the earth’s crust. it formed the ozone layer. it built up in the atmosphere.

Option A

Explanation:

Cyanobacteria were the first organism to produce the most important component of life that is oxygen.

The atmosphere earlier deprived of oxygen due to which there were no multi cellular organism at that time.

Due to the evolution of cyanobacteria there is an evolution of more complex life forms on earth. Multicelluar organism are more complex than unicellular organism that evolved after cyanobacteria.

answer; polycythemia is the correct answer;