Is Life an Unavoidable Planetary Phenomenon Given the Right Conditions?

In this chapter we argue that life, in the form of simple cells, is a common phenomenon in the Universe, given suitable conditions. By contrast, intelligent life, in the sense of organisms having technological capabilities, is probably relatively rare and, in the case of terrestrial life, appears to have been the result of a long, relatively stable geological history of the planet, punctuated by a few key events that affected the whole planet for significant amounts of time, such as the global glaciations of the Proterozoic and the giant asteroid impact at the end of the Cretaceous. Given the subject, “life as a cosmic phenomenon,” we will unavoidably overlap with topics from other chapters in this volume because the conditions for the origin and evolution of terrestrial life are relevant.