The Time Scales of Nucleosynthesis

The nuclei of the atoms of elements heavier than hydrogen are generally believed to have been synthesized in a variety of stars, more or less continuously, throughout the history of the galaxy. The matter ejected from these stars at various stages in their evolution is mixed into the interstellar gas and, in turn, portions of this gas become isolated from the remainder of the galaxy and form later-generation stars such as the sun. The times required for the various stages in the evolution of the matter of our solar system are of interest, both from an astrophysical and a philosophical point of view. We will discuss how relatively definitive information can be obtained on the times for at least the latter stages in this evolution through the measurement of the isotopic composition of those elements in meteorites which contain the daughter products of radioactive decay.