Which of the following living organisms originated first on primitive earth?

Options

A. Aerobic heterotrophs
B. Aerobic autotrophs
C. Anaerobic heterotrophs
D. Anaerobic autotrophs

Answer

To solve the question of which living organisms originated first on primitive Earth, we can follow these steps:

### Step-by-Step Solution

1. **Understand the Conditions of Primitive Earth**:
- Primitive Earth had no free molecular oxygen. This means that aerobic organisms, which require oxygen for respiration, could not survive.

**Hint**: Remember that the absence of oxygen means organisms must adapt to survive without it.

2. **Consider the Type of Respiration**:
- Since there was no oxygen, the organisms that survived would have to perform anaerobic respiration, which does not require oxygen.

**Hint**: Think about how organisms obtain energy in environments lacking oxygen.

3. **Evaluate the Options**:
- The question provides several options, including aerobic and anaerobic organisms. Since aerobic organisms cannot survive in an oxygen-free environment, we can eliminate those options.

**Hint**: Focus on the options that mention anaerobic organisms.

4. **Identify the Nature of the Organisms**:
- We are left with two types of anaerobic organisms: anaerobic heterotrophs and anaerobic autotrophs.
- Heterotrophs obtain energy from organic compounds, while autotrophs produce their own food.

**Hint**: Consider the availability of organic materials in the primitive oceans.

5. **Consider the Environment**:
- The primitive oceans were rich in organic molecules, often described as a "hot dilute soup." This suggests that organisms would need to consume these organic materials to survive.

**Hint**: Think about how the availability of resources influences the type of organisms that could thrive.

6. **Conclude the Most Likely Organism**:
- Given that the conditions favored the presence of organic molecules and the need for energy acquisition through consumption, the first living organisms on primitive Earth would most likely be anaerobic heterotrophs.

**Hint**: Reflect on how early life forms would have adapted to their environment for survival.

### Final Answer
The first living organisms that originated on primitive Earth were **anaerobic heterotrophs**.