Throughout her childhood, Solomon was surrounded by items that contained the synthetic molecules known as CFCs. The compounds were first developed in the 1930s as a commercial coolant, to replace more toxic ammonia and sulfur dioxides, and were included in refrigerators, air conditioners, and other household and industrial items. By the time Solomon reached graduate school at the University of California, Berkeley, in the late 1970s, CFCs were being used in everything from hairspray to foam containers for fast food.

CFCs contain atoms of carbon, fluorine, and chlorine. For example, CFC₁₂, a common refrigerant, has the molecular formula CCl₂Fl₂; this notation indicates that one carbon atom (C) is bound to two chlorine (Cl) and two fluorine (Fl) atoms. By tweaking the balance of these atoms, chemists synthesized CFCs that they believed were stable, nonflammable, and harmless to people and the environment—qualities that led to their broad acceptance.

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Over time, these items emitted CFC molecules into the air; in 1971, British scientist James Lovelock detected CFCs in the atmosphere over England. Since CFCs were considered safe, the news did not raise concern. But it caught the attention of scientist Sherwood Rowland of the University of California, Irvine, who wondered what would happen to this completely synthetic substance in the atmosphere. He and his colleague Mario Molina set out to look for answers.

In 1974, Rowland and Molina proposed that CFCs were not entirely harmless in the atmosphere. Chemists had specifically designed these compounds to be stable, and Molina and Rowland realized that CFCs would stay aloft for a remarkably long time in the atmosphere, residing there and accumulating for 100 years or more. And once in the stratosphere, the molecules would be exposed to UV light so intense that it would break them apart. The process would release solitary chlorine atoms, which previous research had shown could chemically react with—and destroy—ozone, aligning with Farman’s observations from Antarctica. Molina and Rowland calculated that at the rate CFCs were being produced in 1972, the chemicals could destroy 6% of the ozone layer. And manufacturers were making more CFCs every year.

But the scientific view of CFCs didn’t change overnight. Because all conclusions in science are considered open to revision (since our understanding of a concept or process will change as scientists learn more), more evidence was needed to overturn the prevailing conclusion that CFCs were safe.