What was the probable role of oxygen gas in the early stages of life's appearance on Earth?
A) Cellular respiration, which depends on oxygen availability, provided abundant energy to the first life-forms.
B) Oxygen promoted the formation of complex organic molecules through physical processes.
C) Oxygen gas tends to disrupt organic molecules, so its absence promoted the formation and stability of complex organic molecules on the early Earth.
D) Abundant atmospheric oxygen would have created an ozone layer, which would have blocked out ultraviolet light and thereby protected the earliest life-forms.
Answer: C
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