This is an interesting book that perhaps better falls in
the "speculative fact" category rather than "speculative fiction".
The author describes a variety of scenarios in which things on
Earth are different (no Moon, different Earth/Sun masses, different
tides, etc) and how that would affect the planet and life. Though
I obviously haven't put as much thought into it as the author, it
seems clear that trying to write such a book in a comprehensive
fashion is somewhat dangerous. While you may be successful in
predicting one effect, it seems that physical processes on Earth
are intertwined in very subtle ways that we can't possibly imagine.
Comins' treatment of different scenarios comes off as just a little
too neat and tidy. Not simplistic, by any means, but I have
trouble believing in his speculations.
But, hey, if you're going to be a nitpicker, the speculative genre
is hardly a good home for you, so you have to know what to expect.
This book reads like the seeds of several interesting science fiction
novels, and for that reason along, reading it along with a healthy
dose of imagination makes it a lot more fun. Probably the strongest
chapter from my perspective was the one describing what would happen
if a nearby supernova went off...one of the few scenarios in the
book that actually COULD happen. If you're ever bored in a bookstore,
go pick up this book and read Chapter 6 entitled "Antar". It isn't
too long, and it is a frightfully interesting topic.