Exobiology is concerned with four evolutionary epochs: (1) cosmic evolution of biogenic elements and compounds; (2) prebiotic evolution; (3) early evolution of life; and (4) evolution of advanced life. Each of these epochs, briefly described below, represents a major arena of research. Between now and the mid-1990s, the task group expects this conceptual framework to become widely acknowledged and to act as a stimulus for interdisciplinary attacks on exobiological research problems. The first epoch encompasses galactic time and distance scales and involves the death and birth of stars. It begins with the synthesis in stars of the biogenic elements—the elements that make up all life—and their ejection into the interstellar medium; it ends with the distribution of these elements and their compounds throughout our solar system within the planetoids, which became building blocks of planets. Discoveries in carbonaceous meteorites strengthen this perspective, as organic and mineral matter made up of carbon, nitrogen, hydrogen, and oxygen has been found that retains properties traceable to its origins in interstellar clouds and stars.