Question

question 19 of 20 :
select the best answer for the question.

1. what important change in the atmosphere occurred during the proterozoic eon?

a. nitrogen and carbon dioxide levels decreased, fueling bacterial growth.
b. methane levels decreased and oxygen levels increased, promoting aerobic life forms.
c. helium escaped into space and hydrogen was bound into water molecules.
d. carbon dioxide levels increased, causing glaciation that cooled the planet.
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Explanation:

To solve this, we analyze each option:

• Option A: Bacterial growth isn't mainly fueled by decreasing N₂ and CO₂ in Proterozoic. Incorrect.
• Option B: During Proterozoic, cyanobacteria produced O₂, reducing methane (a greenhouse gas) and increasing O₂, which supported aerobic life. Correct.
• Option C: Helium escape and H₂ binding to water isn't a key Proterozoic atmospheric change. Incorrect.
• Option D: CO₂ increase causing glaciation isn't the main Proterozoic atmospheric change. Incorrect.

Answer:

B. Methane levels decreased and oxygen levels increased, promoting aerobic life forms.