Anaerobes were the first organisms to appear on the primitive earth because

Options

A. they had no enzyme system for oxygen utilisation
B. free oxygen could not be assimilated
C. free molecular oxygen was absent
D. they were simple in organisation

Explanation

**Step-by-Step Solution:**

1. **Understanding Anaerobes**: Anaerobes are organisms that do not require oxygen for their survival. They can thrive in environments where oxygen is absent.

2. **Primitive Earth Conditions**: The early Earth was characterized by a lack of free molecular oxygen (O2) in the atmosphere. This means that the environment was anoxic (without oxygen).

3. **Survival of Anaerobes**: Since anaerobes do not need oxygen to survive, they were the first organisms to appear on primitive Earth. They utilized anaerobic respiration processes to generate energy.

4. **Absence of Free Oxygen**: The key reason why anaerobes were the first organisms is that free molecular oxygen was absent in the primitive Earth’s atmosphere. This absence made it impossible for aerobic organisms (which require oxygen) to survive.

5. **Conclusion**: Therefore, the correct answer to the question is that anaerobes were the first organisms to appear on primitive Earth because free molecular oxygen was absent, allowing them to thrive in such an environment.

**Final Answer**: Anaerobes were the first organisms to appear on primitive Earth because free molecular oxygen was absent.

---