How did life begin? Where are all the aliens? For most of human history these questions have been the realm of speculation. Today however, we have rovers on Mars, large space telescopes, and a deep understanding of evolution and biochemistry. So what does the science say? In the episode of the podcast I speak with Professor David Catling, astrobiologist, and planetary scientist at the University of Washington, whose research focuses on understanding the differences between the evolution of planets, their atmospheres, and their potential for life.