Question

Photosynthetic cyanobacteria caused an increase in atmospheric levels of what

Answer 1

Answer: Oxygen.

Explanation:

The photosynthetic cyanobacteria increased the level of oxygen in the environment. Before the evolution of these bacteria there were no oxygen in the marine ecosystem and atmosphere.

But when the these photosynthetic bacteria evolved it started the process of photosynthesis and oxygen was produced as a result of photosynthesis.

Answer 2

Photosynthetic cyanobacteria are capable of producing oxygen as a product of photosynthesis.
It is thought that the rise in oxygen levels in the atmosphere was generated by photosynthetic cyanobacteria during the Archaean and Proterozoic Eras and that reducing atmosphere turned into an oxidizing one.