  Earth is the only planet known to harbor life, therefore we may speculate on
how the nature of the Sun-Earth interaction is relevant to life on Earth, and
how the behavior of other stars may influence the development of life on their
planetary systems. We study the long-term variability of a sample of five solar
analog stars using composite chromospheric activity records up to 50 years in
length and synoptic visible-band photometry about 20 years long. This sample
covers a large range of stellar ages which we use to represent the evolution in
activity for solar mass stars. We find that young, fast rotators have an
amplitude of variability many times that of the solar cycle, while old, slow
rotators have very little variability. We discuss the possible impacts of this
variability on young Earth and exoplanet climates.
