Before revision: However, when porphyrin-based cyanobacteria started to photosynthesize using chlorophyll, dioxygen was released as a byproduct and started to accumulate, first in the ocean and then in the atmosphere.
After revision: However, when porphyrin-based photoautotrophs evolved and started to photosynthesize , which included both the primitive purple bacteria using bacteriochlorophyll and cyanobacteria using chlorophyll, highly reactiveof water splitting dioxygen was released as a byproduct and started to accumulate, first in the ocean and then in the atmosphere.