Where is the ozone layer located and what is its significance for UV radiation?

• A. In the troposphere; it blocks all UV radiation.
• B. In the exosphere; no effect on UV.
• C. In the mesosphere; it blocks UV-A.
• D. In the stratosphere; it filters most UV-B and some UV-C radiation, protecting surface life; ozone depletion increases UV at the surface.

Answer: (D)

The surface-level protective shield against harmful sunlight comes from the ozone layer, which is located in the stratosphere. It absorbs most of the sun’s ultraviolet radiation, especially UV-B and most UV-C, while allowing UV-A to pass through. This filtering greatly reduces the amount of UV reaching the ground, protecting living things from DNA damage, skin cancer, cataracts, and ecological stress. When ozone is depleted, due to human-made chemicals like chlorofluorocarbons, more UV radiation reaches the surface, increasing risks to health and ecosystems. The other layers mentioned don’t provide this concentrated, effective shield in the same way, so they don’t play the same protective role against UV radiation.