Life; An Unauthorised Biography, by Richard Fortey.
As the cover says, this is a natural history of the first 4,000,000,000 years of life on Earth. It is not, as you might suppose, a dull science book, but a fascinating, entertaining and beautifully written book. I'm 3,500 million years in so far, with 1000 million to go (page 77 out of 371). 'Life has now reached a single, large, but complex cell, the kind of small thing that might once have been imagined arising from the progenitive broth'.
The pace picks up from here on!