We construct firm-year level measures of emerging and disappearing work using ads posted between 1940 and 2000 in The Boston Globe, The New York Times, and The Wall Street Journal. Among the set of publicly listed firms, those which post ads for emerging work tend to be younger, more R&D intensive, and have higher future sales and productivity growth. Among all firms, those which post ads for emerging work are more likely to survive and, for privately held firms, are more likely to go public in the future. We develop a model — consistent with the described patterns — with incumbent job vintage upgrading and firm entry and exit. Our estimated model indicates that 55 percent of upgrading occurs through the entry margin, with incumbents accounting for the remaining 45 percent.