I am sure that it was Non cyclic photosynthesis.
Which Came First, Cyclic Photosynthesis Or Non Cyclic Photosynthesis?
Actually it was cyclic photosynthesis. Cyclic photosynthesis does not use oxygen which was key to the organisms at the beginning of time since there was not much oxygen in the atmosphere. Non-cylic photosynthesis came about 2.7 billion years ago when it evolved in the cyanobacteria.
