The first organism were

Options

A. chemoautotrophs
B. chemoheterotrophs
C. autotrophs
D. eukaryotes

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the first organisms on Earth. To answer this, we need to consider the conditions of early Earth and the types of organisms that could have existed during that time.

2. **Analyzing Early Earth Conditions**: Early Earth had a reducing atmosphere, which means it lacked free oxygen. The environment was likely rich in organic molecules, often referred to as "primordial soup," and was characterized by high temperatures.

3. **Identifying the First Organisms**: The first organisms were prokaryotes, which are simple, single-celled organisms. They are believed to have been heterotrophs, meaning they obtained their energy by consuming organic molecules that were available in their environment.

4. **Exploring Modes of Nutrition**: Initially, these prokaryotic organisms relied on fermentation of organic molecules for energy. As they consumed the available organic materials, they eventually led to a depletion of these resources.

5. **Evolution of Autotrophs**: As the organic materials became scarce, some organisms evolved to become autotrophs. These organisms could produce their own organic molecules through processes like chemosynthesis or photosynthesis.

6. **Transition to Eukaryotes**: Over time, as the atmosphere began to change and oxygen levels increased, more complex organisms, known as eukaryotes, emerged. This transition marked a significant step in the evolution of life on Earth.

7. **Conclusion**: Based on the above analysis, the first organisms were likely heterotrophic prokaryotes that obtained energy from organic molecules in a reducing environment.

### Final Answer:
The first organisms were heterotrophic prokaryotes.

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