A Level Chemistry OCR Practice Exam

Which layer of Earth's atmosphere contains the ozone layer?

1. The troposphere

2. The mesosphere

3. The stratosphere

4. The thermosphere

The correct answer is: The stratosphere

The correct answer is the stratosphere, which is the layer of Earth’s atmosphere that contains the ozone layer. The ozone layer plays a crucial role in protecting life on Earth by absorbing the majority of the sun's harmful ultraviolet (UV) radiation. The stratosphere is situated above the troposphere and below the mesosphere, typically extending from about 10 kilometers to about 50 kilometers above the Earth's surface. Within this layer, ozone concentrations increase significantly due to the formation of ozone from oxygen molecules through the action of UV radiation. This unique characteristic of the stratosphere allows it to serve as a critical shield against UV rays, thereby preventing increased incidences of skin cancer and other related health issues. In contrast, the troposphere is the layer closest to Earth where weather phenomena occur, but it contains only a small amount of ozone. The mesosphere, found above the stratosphere, continues up to around 85 kilometers and is where meteors burn up upon entering the Earth's atmosphere, but it is not associated with any significant concentration of ozone. Lastly, the thermosphere, located even higher, is known for its high temperatures and the presence of ionized particles, but it also does not contain the ozone layer. Therefore,