There's a theory that life actually originated not directly through photosynthesis based life, but originally from a very constant source of energy - the earth's crust - Hyperthermophile archaea - using non-oxygen based metabolism which migrated to the surface where photosynthesis evolved and took over as the core energy source.
All laid out in Paul Davies' book - fascinating read: https://www.simonandschuster.com/books/The-Fifth-Miracle/Pau...
replies(6):