Which was not present freely in the early atmosphere of the earth?

Options

A. Water
B. Carbon monoxide
C. Hydrogen
D. Oxygen

Answer

To determine which gas was not freely present in the early atmosphere of the Earth, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Early Earth's Atmosphere**:
- The early atmosphere of Earth was significantly different from what we have today. It was characterized as a "highly reduced atmosphere."

2. **Identifying the Components**:
- The components of the early atmosphere included gases such as methane (CH₄), ammonia (NH₃), nitrogen (N₂), water vapor (H₂O), carbon monoxide (CO), and hydrogen (H₂).

3. **Analyzing the Options**:
- The options provided are:
- A) Water (H₂O)
- B) Carbon monoxide (CO)
- C) Hydrogen (H₂)
- D) Oxygen (O₂)

4. **Recognizing the Absence of Oxygen**:
- Among the options, oxygen (O₂) was not freely present in the early atmosphere. The atmosphere lacked free oxygen, which is essential for aerobic respiration.

5. **Conclusion**:
- The organisms that existed during this time were anaerobic, meaning they did not require oxygen for their metabolic processes. The presence of oxygen became significant only after the emergence of photosynthetic organisms that could produce it.

### Final Answer:
- The gas that was not present freely in the early atmosphere of the Earth is **D) Oxygen (O₂)**.

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