This book was originally Glasgow University Gifford Lectures for the theme The Search for Who We Are in 1985. Sagan does a great job explaining difficult concepts clearly and with compelling evidence. Unfortunately, in several places I also knew about the contrary evidence which undermines his position. That they were not addressed very much disappointed me.
I mentioned this book in my Evidence blog post a few days ago. The search for proof is never ending because new information leads to new questions not satisfactory answers. So why do we continue to search? Because we want to know. Maybe we even feel entitled to know. (I also mentioned it in my Missing Hydrocarbons when I learned the point methane condenses is way out near Saturn not Earth, so why does Earth have life?)