Breakthrough: the changing face of science in America.

Twenty-two years ago, when chemist Mario Molina first warned of damage to Earth's ozone layer, no one took him very seriously. But since the ozone layer protects Earth's inhabitants from the Sun's harmful rays, Molina was determined to prove his point.

In 1974, Molina and other scientists discovered that human-made chemicals called chlorofluoro-carbons (CFCs) were making their way to the ozone layer, 24 kilometers (15 miles) above Earth's surface. Molina did lab experiments to show that CFCs (which were commonly used in refrigerators, air conditioners, and spray cans 20 years ago) destroy ozone. He warned that these chemicals would eventually destroy Earth's protective shield.

Ten years later, when another scientist detected a "hole" in the ozone layer over Antarctica, people began to heed Molina's warnings. In 1987, the United States and many other members of the United Nations signed an international agreement to stop the production of CFCs by this year.

For his work, Molina received the 1995 Nobel Prize in Chemistry. It was the first Nobel Prize ever awarded to a Mexican-American, and the first ever for environmental work. But for Molina, the real reward was that "we were able to convince society to do something about ozone damage."