This is the hypothesis I remember being taught 20 years ago. Rhodopsin, used by phototrophic archea, evolved first and has a broad absorption peak in the green

This is the hypothesis I remember being taught 20 years ago. Rhodopsin, used by phototrophic archea, evolved first and has a broad absorption peak in the green (giving it a purple colour). Chlorophyll evolved to absorb light either side of this peak, in the red and blue.