What a great book for a nerd. Bryson really does try to cover nealy everything in this book, from The Big Bang theory to dinosaurs to human origins and human cells and DNA. This is definitely not an in-depth book on any of these subjects but it gives you enough of a peek into a everything that you can be prodded into doing more research on your own.
Science is a favorite subject for me to read about. There wasn't much of this book that didn't make me a happy camper (except finding out that if you've owned your pillow for more than 6 years, 1/10 of it's weight is live mites, dead mites and mite poop. Guh.). It's written for the layperson, you don't need to be a nerd to appreciate it.
As always, Bryson is a fun writer, making even DNA fun and exciting to read about.