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      Photons Continuously Bombard the Earth

      Energy from the sun comes to the earth in the form of electromagnetic radiation, which is a fancy name for light. Light acts like particles in many ways, and we call these particles photons. Photons are packets of energy, and they are constantly bombarding the earth, which is how the sun's energy reaches us.

      You may not know it, but you can only see a very tiny bit of all the light that is out there. In addition to acting like a particle, light acts like a wave in a lot of ways, and how it behaves depends on its wavelength. The shorter the wavelength, the higher the energy of the light. As you can see on the electromagnetic spectrum below, the light you can see has a wavelength of 300-900 nanometers (nm).

      electromegnetic spectrum

      The electromagnetic spectrum (note: 10-7m = 100 nm).

      UV radiation from the sun being blocked by the ozone layer Longer wavelength light is called infrared radiation. This kind of radiation carries the sun's heat to us, keeping the earth warm. Light with wavelengths shorter than that of visible light is called ultraviolet radiation (UV). Like infrared radiation, UV is invisible to the human eye, but has enough energy to break covalent bonds in biologically important molecules. People who receive excessive doses of ultraviolet radiation have a much greater tendency to suffer irreversible skin damage and skin cancers than people who are not subjected to UV rays.

      On your right you can see a picture showing how the earth is bombarded by UV radiation, shown as dark purple arrows. However, the ozone layer blocks most of the UV radiation. However, a small amount of UV radiation does pass through, shown by the light purple arrows. This small amount is enough to cause sunburn, and in some cases skin cancer. Without the ozone layer, a lot more UV radiation would reach the earth, and this would be very dangerous, to say the least.

        Next: Making and Destroying Ozone

      Image credit

        The earth bombarded by UV radiation: Stanitski, C., Eubanks, L., Middlecamp, C., and Stratton, S. Chemistry in Context, 3rd ed. New York: McGraw-Hill, 2000.

      Copyright ©2001 The Chemical Heritage Foundation