Answer;
- Oxygen
-Ancient cyanobacteria released oxygen, which assisted in creating the atmosphere as we know it today.
Step-by-step explanation;
-The oxygen atmosphere that we depend on was generated by numerous cyanobacteria during the Archaean and Proterozoic Eras.
-Cyanobacteria are aquatic and photosynthetic, meaning they live in the water, and can manufacture their own food. During the process of photosynthesis, energy from sunlight is used together with carbon (iv) oxide and water to form organic molecules that serve as nutrients for the organisms and also oxygen gas is released to the atmosphere.