If the only organisms on earth that perform photosynthesis were bacteria with only one photosystem, which perform cyclic photophosphorylation, the resulting environment wouldn't be capable of supporting animal life as we know it because cyclic photophosphorylation does not lead to the generation of oxygen.
So this type of phosphorylation will not produce oxygen for animals and humans, and even plants to live on, and thus these organisms wouldn't be suitable for sustaining life on earth on their own. There has to be "regular" plants with "regular" photosynthesis as well.
