VIEW: Ozone Hole

Earth receives energy from the Sun in the form of electromagnetic radiation. A small portion of this radiation arrives as heat, while another small portion arrives as visible light. These two forms of energy make life on Earth possible. Another higher frequency form of electromagnetic radiation, called ultraviolet (UV) light, strikes Earth as well. However, rather than supporting life, UV light is known to damage the tissues, cells, and genetic material of living organisms and is linked to skin cancer, cataracts, and suppression of the immune system in humans.

Fortunately, gases in Earth's atmosphere absorb the majority of UV light and convert it to heat, rendering it harmless before it can reach Earth's surface. The gas responsible for most UV light absorption in the atmosphere is ozone. Ozone molecules are made up of  three oxygen atoms. It is a little different from the molecules of oxygen living things breathe; this type of oxygen molecule has only two oxygen atoms. When UV light strikes an ozone molecule, the energy splits the molecule into one two-atom oxygen molecule and one free oxygen atom, releasing heat in the process. Ozone in Earth's atmosphere can absorb up to 98% of the sun's UV light. 

Scientists discovered that chlorine-based compounds called CFCs destroyed ozone. In fact, scientists now know that a single chlorine atom from a CFC molecule can destroy more than 100,000 ozone molecules!   By the 1980s, scientists had discovered that the ozone concentrations in the atmosphere over Earth's poles had been drastically reduced.  This led to many countries signing the Montreal Protocol in 1987, to ban the use of CFCs. 

After you have completed this part of the lesson, you can check the associated box on the main course page to mark it as complete