What was the nature of first photoautotrophs-oxygenic or anoxygenic?

Explanation

### Step-by-Step Solution:

1. **Understanding Photoautotrophs**:
- Photoautotrophs are organisms that can produce their own food using light energy. They utilize sunlight to convert carbon dioxide and water into glucose and oxygen through photosynthesis.

2. **Defining Oxygenic and Anoxygenic**:
- **Oxygenic Photoautotrophs**: These are organisms that produce oxygen as a byproduct of photosynthesis. Examples include plants, algae, and cyanobacteria.
- **Anoxygenic Photoautotrophs**: These organisms do not produce oxygen during photosynthesis. Instead, they may use other substances, such as hydrogen sulfide, to carry out their metabolic processes.
...