The oldest fossil record of blue-green algae is 2.9 billion years old. It is

Options

A. Stromatolites
B. Archaeospheroids
C. Archaeopterix
D. Chlamydomonas

Answer

To answer the question regarding the oldest fossil record of blue-green algae, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Blue-Green Algae**:
- Blue-green algae are also known as cyanobacteria. They are photosynthetic microorganisms that can produce oxygen as a byproduct of photosynthesis.

2. **Historical Context**:
- The question states that the oldest fossil record of blue-green algae is 2.9 billion years old. This indicates that these organisms have existed for a significant period in Earth's history.

3. **Significance of Cyanobacteria**:
- Cyanobacteria are crucial in the history of life on Earth because they were among the first organisms to perform oxygenic photosynthesis, which contributed to the increase of oxygen in the atmosphere.

4. **Identifying the Fossil Record**:
- The specific fossil record mentioned is that of Archaeospheroids, which is recognized as the oldest known cyanobacteria fossil.

5. **Conclusion**:
- Based on the information provided, the answer to the question is that the oldest fossil record of blue-green algae (cyanobacteria) is of Archaeospheroids, which is 2.9 billion years old.

### Final Answer:
The oldest fossil record of blue-green algae is 2.9 billion years old, and it is of Archaeospheroids.

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