The layer of the Earth's atmosphere that surrounds us is called the troposphere. The stratosphere, the next higher layer, extends about 10–50 kilometers above the Earth's surface. Stratospheric ozone is a naturally occurring gas that filters the sun's ultraviolet (UV) radiation. A diminished ozone layer allows more radiation to reach the Earth's surface. For people, overexposure to UV rays can lead to skin cancer, cataracts, and weakened immune systems. Increased UV can also lead to reduced crop yield, disruptions in the marine food chain, and other harmful effects.

 

 

In the late 1970s scientists discovered that chemicals like Chlorofluorocarbons (CFCs) and Carbon mono oxide (CO) could destroy the Ozone layer. Chlorofluorocarbon is a gas used in air conditioning, refrigerator and aerosol spray propellants. It was invented by Thomas Midgley in 1928. Studies showed that CFC molecules are heavier than nitrogen or oxygen molecules, it takes around 15 years to reach to the upper atmosphere from ground level and can stay there for centuries. During the stay in the upper atmosphere CFC’s break down into free radical catalysts (Chlorine, Bromine, hydroxyl radical and nitric oxide), these catalysts further react with ozone gas molecules and results in the thinning of the ozone gas layer. Eventually the ozone gas thins out so much it creates a hole leaving the planet and its inhabitants vulnerable to ultraviolet radiation from the sun.