A new theoretical framework for interpretation was advanced during the 1970s when Donald D. Clayton rejected the popular belief among meteoriticists that the solar system began as a uniform hot gas. Instead he predicted that unusual but predictable isotopic compositions would be found within thermally condensed interstellar grains that had condensed during mass loss from stars of differing types. He argued that such grains exist throughout the interstellar medium. Clayton's first papers using that idea in 1975 pictured an interstellar medium populated with supernova grains that are rich in the radiogenic isotopes of Ne and Xe that had defined the extinct radioactivities. Clayton defined several different types of stardust presolar grains likely to be discovered: "stardust" from red giant stars, "sunocons" (acronym from "SU"per"NO"va "CON"densates) from supernovae, "nebcons" from nebular condensation by accretion of cold cloud gaseous atoms and molecules, and "novacons" from nova condensation. Despite vigorous and continuous active development of this picture, Clayton's suggestions lay unsupported by others for a decade until such grains were discovered within meteorites.