With the aid of marine water's magnesium porphyrin, some selected chemoautotrophs would have finally produced pigments similar to chlorophyll.
These pigments are bacteriochlorophylls, which to produce real chlorophyll, would have essentially undergone a few alterations.
Primitive autotrophs would have developed as a result of the same.
With time, these rudimentary autotrophs improved their ability to produce food through photosynthesis and started releasing free molecular oxygen into the environment.
The oxygen revolution refers to this transformative development in early earth history.