Authors Seth Cagin and Philip Dray. Their new book is "Between Earth and Sky: How CFCs Changed Our World and Endangered the Ozone Layer." It's about how CFCs (or chlorofluorocarbons) went from being the "miracle compound" to the the biggest threat to the ozone layer. CFCs came into being in 1928 and made possible the mass use of refrigerators and air conditioners. By the 1950s they were used in aerosol sprays and in the manufacture of Sytrofoam. But by 1974, scientists began to see their deleterious environmental effects.