Stephenson continues to very deservedly sit at the top of my "favorite current authors" list. This one is almost two separate books: the first 2/3 dealing with humanity's coping with a planet wide extinction level event; the last third picking up five millennia later. As usual, he is amazingly skilled at presenting very complex subjects (such as orbital dynamics, just one possible example in this book) in very understandable ways. From possible ways of moving out off of our planet to how we would deal with a global catastrophe, there's a lot to digest, but it's well worth doing.