First aerobic photoautotrophs developed around

Options

A. 3.8-4.0 billion years ago
B. 3.5-3.8 billion years ago
C. 3.3-3.5 billion years ago
D. 2.8-3.2 billion years ago

Answer

To determine when the first aerobic photoautotrophs developed, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Types of Autotrophs**:
- The first autotrophs were anoxygenic, meaning they did not produce oxygen during photosynthesis. They did not use water as a raw material.
- Later, some autotrophs evolved to become oxygenic, which means they used water in photosynthesis and released oxygen as a byproduct.

2. **Identify the First Oxygenic Photoautotrophs**:
- The first oxygenic photoautotrophs are known to be cyanobacteria. These organisms are significant because they were the first to produce oxygen through photosynthesis.

3. **Determine the Timeframe for Cyanobacteria**:
- Scientific evidence suggests that cyanobacteria evolved approximately 3.3 to 3.5 billion years ago. This timeframe is crucial as it marks the transition to aerobic (oxygen-producing) photosynthesis.

4. **Analyze the Given Options**:
- The options provided are:
1. 3.8 to 4.0 billion years ago
2. 3.5 to 3.8 billion years ago
3. 3.3 to 3.5 billion years ago
4. 2.8 to 3.2 billion years ago
- Based on our understanding, the correct timeframe for the emergence of the first aerobic photoautotrophs (cyanobacteria) is 3.3 to 3.5 billion years ago.

5. **Select the Correct Answer**:
- Therefore, the correct answer to the question is option 3: **3.3 to 3.5 billion years ago**.

### Final Answer:
The first aerobic photoautotrophs developed around **3.3 to 3.5 billion years ago**.

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