One of the following appeared on the earth with the coming of the plants and was absent in the past

Options

A. Carbon dioxide
B. Methane
C. Ammonia
D. Oxygen

Answer

To solve the question "One of the following appeared on the earth with the coming of the plants and was absent in the past," we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Context**: The question is asking about a substance that became present on Earth with the advent of plants. This implies that we need to consider the role of plants in the environment, particularly their metabolic processes.

2. **Analyze the Options**: The options given are:
- Carbon dioxide (CO2)
- Methane (CH4)
- Ammonia (NH3)
- Oxygen (O2)

3. **Review the Role of Plants**: Plants are known to perform photosynthesis, a process where they convert carbon dioxide and water into glucose and oxygen, using sunlight. This process is crucial for the production of oxygen in the atmosphere.

4. **Evaluate Each Option**:
- **Carbon Dioxide**: This gas was present in the atmosphere before the emergence of plants, as it is a product of respiration and combustion.
- **Methane**: Methane was also present in the early atmosphere, produced by anaerobic decomposition.
- **Ammonia**: Ammonia was present due to various geological and biological processes.
- **Oxygen**: Free oxygen was not present in significant amounts in the early atmosphere. It began to accumulate in the atmosphere as a byproduct of photosynthesis carried out by plants.

5. **Conclusion**: Based on the analysis, the gas that appeared on Earth with the coming of plants and was absent in the past is **Oxygen (O2)**.

### Final Answer:
The correct option is **Oxygen**.

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