Question

Which of the following gases was not present in the early period of the Earth?

• A. O2
• B. CO2
• C. H2
• D. N2

Hint:

The early Earth's atmosphere was mostly carbon dioxide, nitrogen, and hydrogen, with oxygen levels rising much later due to photosynthesis.

Answer 1

The Correct Option is A

Step 1: Understand the Earth's early atmosphere.
In the early stages of Earth's formation, the atmosphere was vastly different from today. It was mainly composed of gases like carbon dioxide (CO2), hydrogen (H2), and nitrogen (N2), with little to no oxygen (O2) present. The rise in oxygen levels was a result of photosynthetic organisms, which began to release oxygen into the atmosphere.
Step 2: Review the options.
- O2 was not present in significant amounts in the early atmosphere. - CO2, H2, and N2 were prevalent during Earth's early history.
Step 3: Conclude.
Oxygen (O2) was absent in large quantities in the early Earth's atmosphere, making option (A) the correct answer.
Final Answer: \[ \boxed{\text{O2}} \]