It is estimated that mainly ..... of thee earth's terrestrial surface is covered by lichens .

Options

A. `18%`
B. `12%`
C. `8%`
D. `4%`

Answer

To solve the question regarding the percentage of the Earth's terrestrial surface covered by lichens, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Lichens**: Lichens are symbiotic organisms made up of fungi and algae or cyanobacteria. They are known for their ability to survive in harsh environments and are often found in areas with low pollution levels.

2. **Role of Lichens**: Lichens serve as indicators of environmental health, particularly air quality. They are sensitive to pollution, which makes their presence a sign of a clean environment.

3. **Pioneer Species**: Lichens are considered pioneer species because they can colonize bare substrates, such as rocks. They contribute to soil formation by breaking down the rock surface, allowing other plants to grow later.

4. **Coverage Estimation**: According to various studies and surveys, lichens are estimated to cover approximately 6-8% of the Earth's terrestrial surface.

5. **Selecting the Correct Answer**: Based on the information provided, the most accurate estimate for the coverage of lichens on the Earth's terrestrial surface is 8%. Therefore, the correct answer is the option that states 8%.

### Final Answer:
The estimated coverage of lichens on the Earth's terrestrial surface is **8%**.

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