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BIO NMDCAT Concept of Evolution
nmdcat.online July 14, 2026

2. A scientist claims that free oxygen was abundant in Earth’s primitive atmosphere. Which observation most strongly contradicts this claim?

A. Organic molecules are easily oxidized by oxygen.
✓
B. Volcanoes release carbon dioxide.
C. Oceans contain dissolved salts.
D. Modern plants produce oxygen.

📝 Explanation

Correct: Free oxygen would have oxidized newly formed organic molecules, preventing their accumulation. B: Does not contradict the claim. C: Unrelated. D: Oxygen production by plants occurred much later. Concept: Primitive atmosphere and chemical evolution.

📖 Additional Information

  • Organic molecules are easily oxidized by oxygen.
  • Volcanoes release carbon dioxide.
  • Oceans contain dissolved salts.
  • Modern plants produce oxygen.

Correct: Free oxygen would have oxidized newly formed organic molecules, preventing their accumulation. B: Does not contradict the claim. C: Unrelated. D: Oxygen production by plants occurred much later. Concept: Primitive atmosphere and chemical evolution.

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