Who were first oxygenic and aerobic photoautotrophs ?

Explanation

**Step-by-Step Solution:**

1. **Identify the Organisms**: The first organisms to be recognized as oxygenic and aerobic photoautotrophs are cyanobacteria.

2. **Understand the Definition**: Cyanobacteria are often referred to as blue-green algae. They are capable of photosynthesis, which allows them to convert light energy into chemical energy.

3. **Timeline of Evolution**: Cyanobacteria evolved approximately 3,300 to 3,500 million years ago. This places their origin in the early history of life on Earth.

...