Question

precambrian - 3500 to 545 mya

• emergence of unicellular photosynthetic organisms 3.0 to 2.5 billion years ago
• oxygen began to accumulate in the atmosphere
• first multicellular eukaryotic organisms: green algae—1.2 billion years ago

value: 7
the biggest change in the earth was the accumulation of ______ in the
atmosphere.
○ a. nitrogen
○ b. smog
○ c. carbon dioxide
○ d. carbon monoxide
○ e. oxygen
○ f. argon

Explanation:

The text mentions "Oxygen began to accumulate in the atmosphere" as a significant event during the Precambrian. Among the options, oxygen is the gas that started accumulating as per the given information. Nitrogen has always been a major component (but not the one newly accumulating as per the context here). Smog is a modern - day air pollution phenomenon. Carbon dioxide was likely present in different amounts but the key point from the text is oxygen accumulation. Carbon monoxide is a toxic gas not related to this large - scale atmospheric change described. Argon is a noble gas and not the focus of the text's atmospheric change description.

Answer:

e. Oxygen