Cyanobacteria were important for earth's early atmosphere because they produce during respiration. question 1 options: nitrogen oxygen water carbon dioxide

Cyanobacteria were important for Earth's early atmosphere because they produce oxygen.  

Explanation:  

Cyanobacteria is a Phylum consists of the free living bacteria and endosymbiosis. Cyanobacteria is also called blue green algae which obtain energy through oxygenic photosynthesis and releases Oxygen gas in the atmosphere. Cyanobacteria is responsible for the early oxygen production in environment which changed the early reducing atmosphere of the earth into the oxidizing atmosphere that causes the event of great oxygenation that is rusting of the earth. During this period most of the anaerobes extinct or evolve to live as a parasite or symbol on in other hosts.                      

the correct option is option d

not too sure but maybe in the hot springs.