When I was growing up, the science of extraterrestrial life was called exobiology. This was a difficult area of research since there was no evidence of any subject matter, and the term fell into disrepute. The modern successor is called astrobiology, which may still not be the best name. Anyhow, the idea is to study the possibility of life out there in all its contexts, to look at both the nature of the universe and how life developed and survives here on Earth to see what might be possible.
This book demonstrates the new approach to a "t." After an introductory chapter that attempts to define life, the second chapter, entitled "Origins of a Habitable Universe," provides the best summary I've ever read of how the universe began and developed in its early stages, leading to how stars form and evolve. The story continues in the third chapter ("Origins of a Habitable Planet"), which covers how the solar system and eventually the Earth formed. The next four chapters start with chemistry and end with biology, going from discussing the basic chemical reactions that might have occurred on the early Earth and trying to work out how this led to life. And, once there was life, how it developed over time into ever more sophisticated and complex creatures, changing its environment along the way, as the invention of photosynthesis led to an atmosphere steeped with caustic oxygen, a nasty substance to early life but essential to the active metabolism of modern animals. The chemistry discussion is the single strongest portion of the book, not too surprising since one of the authors is a chemist.
The final chapters become more topical: extremophiles (life that exists in places you'd think were too nasty to support life), a survey of conceivably habitable areas of our solar system (and beyond), and, finally, the search for extraterrestrial life from the Viking missions (another excellent discussion, this time of the Viking biology experiments and their mixed conclusions) to the Mars meteorite to SETI.
There are maybe half-a-dozen truly great questions in science: How did the universe begin? How did it end? How did life begin? Are we alone? If there's any one science that ties all of these together, it's astrobiology. As our tools grow more sophisticated, and as we grow ever more capable of answering these questions, astrobiology will become ever more significant. Look for headlines worldwide on the day when - as this book predicts - we detect oxygen in the atmosphere of an alien planet, something that (so far as we know) could only be caused by life.
And if you want to be ready for that day, read this book. It covers all the relevant topics in clear and entertaining prose, always remaining comprehensible despite the sometimes arcane issues but never skimping on technical detail. You can read it quickly (as I had to do since it was a library book I'd been slow to get started on) and get the gist of a matter, or take your time to read carefully in order to truly understand what's going on (as I could do only a couple of times).
The copy of this book I have in hand is actually from my local library; however, I want this book by my side for further study and as a reference. I will definitely be buying a copy (if I don't get it for Christmas, that is!). I recommend this book highly to anyone interested in one of the most significant fields of scientific study there is. (Note that I don't give out five stars very often.)