It is believed that the organisms first inhabited Earth's surface were :

Options

A. saprotrophs
B. autotrophs
C. chemoheterotrophs
D. none of these

Answer

To solve the question "It is believed that the organisms first inhabited Earth's surface were:", we will analyze the options provided and the characteristics of the organisms mentioned.

### Step-by-Step Solution:

1. **Understand the Options**: The options given are:
- A) Septotrophs
- B) Autotrophs
- C) Chemoheterotrophs
- D) None of these

2. **Define the Terms**:
- **Septotrophs**: These are organisms that feed on non-living organic matter (detritus). They are also known as detritivores.
- **Autotrophs**: These organisms can synthesize their own food from inorganic substances (like plants).
- **Chemoheterotrophs**: These organisms obtain their energy and carbon from organic compounds. They cannot produce their own food and rely on other organic sources.
- **None of these**: This option implies that none of the previous answers are correct.

3. **Consider the Primitive Earth Conditions**: The early Earth had a reducing atmosphere with no free oxygen, but it was rich in water vapor, carbon dioxide, nitrogen, and hydrogen. Under these conditions, complex organic molecules formed, which served as a source of carbon and energy.

4. **Identify the First Life Forms**: The first life forms likely utilized available organic compounds for energy. Since they could not synthesize their own food, they would be classified as heterotrophs. Among heterotrophs, those that derive their energy from organic compounds are known as chemoheterotrophs.

5. **Evaluate the Options**:
- **Septotrophs**: Not the first life forms as they feed on dead organic matter.
- **Autotrophs**: Not likely the first, as they synthesize their own food.
- **Chemoheterotrophs**: This is the most plausible option as they rely on organic compounds for energy.
- **None of these**: This option is incorrect since we have identified a suitable category.

6. **Conclusion**: Based on the analysis, the organisms that first inhabited Earth's surface were **Chemoheterotrophs**.

### Final Answer:
The organisms that first inhabited Earth's surface were **Chemoheterotrophs**.

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