Answer: The correct answer is-
C.They replaced carbon dioxide with oxygen in the atmosphere.
Cyanobacteria ( also known as blue green algae) is a large phylum of bacteria that is capable of synthesizing its own food using carbon dioxide and water in the presence of sunlight ( photosynthesis).
They contain a green pigment called chlorophyll that absorbs energy from sunlight and helps in the formation of food ( glucose). They release oxygen as a byproduct in the atmosphere.
As these organisms utilize carbon dioxide ( that is present in the atmosphere) to give oxygen in return, therefore, they affected early atmosphere of Earth by replacing carbon dioxide with oxygen.
Thus, option C) is the right answer.
The answer is B I believe!
