EvolutionEasyBloom L3
Question
The atmosphere of early earth probably contained no O₂ until the emergence of organisms that...
Options
A.were chemoautotrophic.
B.were oxygen-respiring.
C.used hydrogen sulphide as a hydrogen source for photosynthesis.
D.used water as a hydrogen source for photosynthesis.
Solution
Sol.(d) [Key Concept: Early Earth — O₂ from Water-splitting Photosynthesis] Around 2.5 billion years ago, during the Precambrian, oxygen began to accumulate in the atmosphere due to the action of photosynthetic cyanobacteria that used water (H₂O) as a hydrogen source for photosynthesis, releasing O₂ as a byproduct. This oxygenic photosynthesis fundamentally changed Earth's atmosphere.
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