alleryWhich organisms caused the Great Oxygenation Event through photosynthesis?
ACyanobacteria
BGiant dinosaurs
CFlowering plants
DEarly mammals
Answer & Solution
Correct answer: A. Cyanobacteria
1. Oxygen rose because of photosynthesis by early life.
2. About a billion years of cyanobacterial photosynthesis led to it.
3. Flowering plants, dinosaurs and mammals came far later.
_Source: Wikipedia, Atmosphere of Earth, Second atmosphere_
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