Answer:
Oxygen, origin of plants and chloroplast.
Explanation:
The oxygen present in our atmosphere was generated by various species of cyanobacteria during the Archaean and Proterozoic Eras. origin of plants on the earth is other great contribution of the cyanobacteria. The chloroplast which is present in plants due to which they make their own food is actually a cyanobacterium living within the plant's cells.
