The first organisms appeared on earth were

Options

A. Chemoheterotrophs
B. Chemoautotrophs
C. Photoautotrophs
D. Decomposers

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the first organisms that appeared on Earth. We need to identify the correct type of organism from the given options: chemoheterotrophs, chemoautotrophs, photoautotrophs, or decomposers.

2. **Identifying the Era**: The first organisms appeared during the Archaeozoic era, which is known for the existence of unicellular organisms. This era is crucial in understanding the timeline of life's evolution on Earth.

3. **Characteristics of First Organisms**: The first organisms were unicellular and prokaryotic. Prokaryotes are the simplest forms of life, lacking a nucleus and complex organelles.

4. **Nutritional Mode**: The first organisms were chemoheterotrophs. This means they could not synthesize their own food and relied on organic matter for nutrition. During the Archaeozoic era, the primary source of organic matter was found in the deep sea.

5. **Eliminating Other Options**:
- **Chemoautotrophs**: These organisms can synthesize their own food using chemical substances and appeared later in the evolutionary timeline.
- **Photoautotrophs**: These are organisms that use sunlight for photosynthesis (like green plants) and evolved much later than the first organisms.
- **Decomposers**: These organisms feed on dead organic matter, but during the Archaeozoic era, only simple unicellular organisms existed, and thus decomposers were not present.

6. **Conclusion**: Based on the information gathered, the correct answer to the question is that the first organisms to appear on Earth were **chemoheterotrophs**.

---