What has led to formation of ozone holes?

Explanation

### Step-by-Step Solution:

1. **Understanding the Ozone Layer**:
- The ozone layer is a region of Earth's stratosphere that contains a high concentration of ozone (O₃) molecules. It acts as a protective shield against harmful ultraviolet (UV) radiation from the sun.

2. **Importance of the Ozone Layer**:
- The ozone layer is crucial because it protects living organisms from UV radiation, which can cause skin cancer and other health issues by damaging DNA and proteins.

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