Which of the following describes the importance of cyanobacteria to early Earth atmosphere formation?

Which of the following describes the importance of cyanobacteria to early Earth atmosphere formation?
A.) Cyanobacteria released oxygen into the air, creating a protective ozone layer
B.) Cyanobacteria relased nitrogen into the air, creating a protective ozone layer
C.) Cyanobacteria absorbed excess oxygen from the air, creating proper amounts of atmospheric oxygen
D.) Cyanobacteria absorbed excess carbon dioxide from the air, creating a protective ozone layer