If Early Earth's Atmosphere Contained Little or No O₂, Then

question 60

Multiple Choice

If early Earth's atmosphere contained little or no O₂, then where did most of the O₂ in our modern atmosphere come from?

• A) Respiration
• B) The oxidation of metals
• C) Photosynthesis
• D) The breakdown of carbon dioxide
• E) The splitting of water vapor by sunlight

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