photosynthesis nitrogen fixation sulfur reduction aerobic respiration
I gave my students this multiple choice question: The saturation of surface rock with oxygen early in Earth's history reflected a change in Earth's atmosphere. This change directly made which life process possible?

Only one answer is correct among these 4 choices:
- photosynthesis
- nitrogen fixation
- sulfur reduction
- aerobic respiration

Could you tell me which one is correct?

aerobic respiration