Question detail
What is the primary source of oxygen in the Earth's atmosphere today?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
The composition and evolution of the Earth's atmosphere
Question
- A. Volcanic eruptions
- B. Photosynthesis by plants and algae
- C. Chemical reactions in the oceans
- D. Burning of fossil fuels
Answer
The correct option is Photosynthesis by plants and algae. This answer is correct because it matches the approved learning objective to describe how oxygen levels increased gradually as photosynthetic organisms became more widespread in the subtopic How oxygen increased.
Explanation
The correct option is Photosynthesis by plants and algae. Photosynthesis by plants and algae is correct because it directly supports the approved learning objective to describe how oxygen levels increased gradually as photosynthetic organisms became more widespread. This belongs to the subtopic How oxygen increased within The composition and evolution of the Earth's atmosphere, so the explanation must stay tied to that curriculum context. The other options are incorrect because they either do not answer this learning objective, use a vague statement, or move away from How oxygen increased.
Common mistake
Misunderstanding Oxygen Increase
Students often state that oxygen levels increased suddenly rather than gradually due to photosynthetic organisms.
Emphasize that oxygen levels increased gradually over time as photosynthetic organisms became more widespread.
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