The thinning of the ozone layer is believed to have begun in

Options

A. 1890
B. 1953
C. 1975
D. 1981

Answer

**Step-by-Step Solution:**

1. **Understanding Ozone Layer**: The ozone layer is a region of Earth's stratosphere that contains a high concentration of ozone (O3) and is crucial for protecting life on Earth by absorbing the majority of the sun's harmful ultraviolet (UV) radiation.

2. **Formation of Ozone**: Ozone is formed when oxygen molecules (O2) interact with nascent oxygen (O) in the atmosphere. The chemical formula for ozone is O3.

3. **Causes of Ozone Depletion**: The depletion of the ozone layer is primarily caused by human-made chemicals, particularly ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs) and halons.

4. **Historical Context**: The thinning of the ozone layer began to be observed in the late 1970s. This period marks the beginning of significant concern regarding ozone depletion due to the release of ODS into the atmosphere.

5. **Evaluating Options**:
- **1890**: This option is incorrect as there was no awareness or significant evidence of ozone depletion at that time.
- **1953**: This option is also incorrect as the issue was not recognized until later.
- **1975**: This option is correct because it falls within the late 1970s when the thinning of the ozone layer was first observed.
- **1981**: This option is incorrect as it is after the initial observations of ozone depletion.

6. **Conclusion**: Based on the information and historical context, the thinning of the ozone layer is believed to have begun in **1975**.

**Final Answer**: 1975

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