alleryStart learning →Free oxygen first built up in Earth's air as a waste product of which process?
AVolcanic eruption
BPlate subduction
CPhotosynthesis
DMeteor impacts
Answer & Solution
Correct answer: C. Photosynthesis
1. Early Earth had abundant carbon dioxide and no oxygen gas at all.
2. Blue-green algae took in carbon dioxide and gave out oxygen as waste.
3. That process is photosynthesis, and it slowly stocked the air with oxygen.
_Source: OpenStax Astronomy (CC BY 4.0), section 8.4 Life, Chemical Evolution, and Climate Change_
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