Which was absent is the atmospher at the time of origin of life ?

Options

A. `NH_(3)`
B. `H_(2)`
C. `O_(2)`
D. `CH_(4)`

Explanation

### Step-by-Step Solution:

1. **Understanding the Origin of Life**: The origin of life is often explained through the theory of chemical evolution or abiogenesis, which suggests that life arose from simple organic compounds.

2. **Identifying the Atmosphere Components**: At the time of the origin of life, certain atoms and molecules were present in the atmosphere. Key elements included carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S).

3. **Conditions of the Early Earth**: The early Earth had high temperatures and was characterized by anaerobic conditions, meaning there was little to no free oxygen in the atmosphere. This environment was reducing, which facilitated the formation of simple organic compounds.

4. **Formation of Simple Molecules**: Under these conditions, simple molecules such as water (H2O), hydrogen (H2), methane (CH4), and ammonia (NH3) were formed from the available elements.

5. **Absence of Oxygen**: Oxygen was notably absent in the early atmosphere. The presence of oxygen would have created an oxidizing environment, which would hinder the formation of the complex organic molecules necessary for life.

6. **Conclusion**: Therefore, the correct answer to the question "Which was absent in the atmosphere at the time of origin of life?" is oxygen.

### Final Answer:
**Oxygen was absent in the atmosphere at the time of the origin of life.**

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