Which type of radiation is largely blocked by Earth's atmosphere?

• A. Infrared radiation.
• B. Ultraviolet radiation.
• C. Visible light.
• D. Radio waves.

Answer: (B)

Earth's atmosphere acts as a shield against Sunlight, especially high-energy ultraviolet radiation. The ozone layer in the upper atmosphere and oxygen molecules absorb most of the short-wavelength UV photons, particularly UV-C and much of UV-B. Because of this absorption, only a small fraction of UV reaches the surface, which helps protect living organisms from DNA damage and harmful effects.

Visible light and radio waves pass through the atmosphere with little attenuation, which is why we can see the Sun and communicate. Infrared radiation is largely absorbed by greenhouse gases like water vapor and carbon dioxide, though not as completely as ultraviolet, so some infrared can still reach the surface.