    ‘Séntence 1: When, - did ° photosynithetic  organisms cuolve,on Barth?    Sentence 23. Freé -oxygen -gas’ ris, almost             noneaistent in Earth's. aimospheie. before    photosijnilietic archaea and’ bac           a ewok  probably, about, 3.5°billion years’ aga  * : :    *    