In 1974, Molina hypothesized that chlorofluorocarbons, or CFCs, then a widely used ingredient of aerosol cans, air conditioners, and refrigerators, were depleting the ozone layer, a thin shield of gas some ten to twenty-five miles above the earth's surface.
Stratospheric ozone protects the planet from the sun's harmful ultraviolet rays.
Without it, plant and animal life as we know it could not exist on the planet, at least on land. Molina predicted that a single atom of chlorine, released by the breakup of CFCs in the upper atmosphere, could destroy up to 100,000 molecules of ozone. But by 1979, he had proven his theory. Molina testified before Congress, and the number of letters that poured in was second only to the number received by Congress about the Vietnam War. Bowing to pressure, manufacturers started to look for alternatives to CFCs.