CFCs (chlorofluorocarbons), which were used extensively as refrigerants (used to cool objects) and propellants (the gases used in spray cans to pressurize the can and shoot the substance out), were found to be greatly detrimental to life on Earth because of its effects on the atmosphere.
The chemical components of CFC cause it to get rid of the ozone in our atmosphere. The ozone, or O₃, is replaced by other gases when reacting with CFCs. This can greatly harm life on Earth because the layer of ozone in our atmosphere acts as a natural "sunscreen" for the Earth; it blocks large amounts of UV radiation from the sun. Without the ozone layer, lethal levels of radiation would be able to reach the Earth's surface and cause great damage to most life forms. This is the reason why the widespread use of CFCs was stopped.
