What important change in the atmosphere occurred during the Proterozoic Eon?
A. Helium escaped into space and hydrogen was bound into water molecules
B. Nitrogen and carbon dioxide levels decreased, fueling bacteria growth
C. Carbon dioxide levels increased, causing glaciation that cooled the planet
D. Methane levels decreased and oxygen levels increased, promoting aerobic life forms
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What important change in the atmosphere occurred during the Proterozoic Eon?
A. Helium escaped int...
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