Atmosphere of earth just before the origin of life consisted of

Options

A. Water vapour, `CH_4,NH_3` and oxygen
B. `CO_2,NH_3" and "CH_4`
C. `CH_4,NH_3,H_2` and water vapours
D. `CH_4,O_3,O_2` and water vapours

Answer

**Step-by-Step Solution:**

1. **Understanding the Context**: The question asks about the composition of Earth's atmosphere just before the origin of life. It is important to note that this period is characterized by a lack of free oxygen.

2. **Identifying Key Components**: The atmosphere before life was considered to be "reducing," meaning it had very little oxygen. Instead, it was rich in other gases.

3. **Listing the Gases**: The primary gases present in the Earth's early atmosphere included:
- Methane (CH₄)
- Ammonia (NH₃)
- Hydrogen (H₂)
- Water vapor (H₂O)

4. **Excluding Oxygen**: It is crucial to highlight that oxygen (O₂) was not a significant component of the atmosphere at this time, as it was produced later through photosynthesis.

5. **Considering Additional Gases**: While nitrogen (N₂) and carbon dioxide (CO₂) may have been present, they were not the dominant gases in the atmosphere before life began.

6. **Evaluating the Options**: Given the options provided:
- Option 1: Water vapor, methane, ammonia, and oxygen (Incorrect - oxygen was not present)
- Option 2: Carbon dioxide, ammonia, and methane (Incorrect - missing hydrogen and water vapor)
- Option 3: Methane, ammonia, hydrogen, and water vapor (Correct - includes the key components)
- Option 4: Any other combination that includes oxygen or omits hydrogen and water vapor (Incorrect)

7. **Conclusion**: The correct answer is that the atmosphere of Earth just before the origin of life consisted of methane, ammonia, hydrogen, and water vapor.

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