The Long Mars by Terry Pratchett/Stephen Baxter
Baxter and Pratchett continue their Long Earth series with this latest book. It is now 2040 and Yellowstone
has erupted causing most of the prime earth's population to flee to stepwise earths. At the same time, super-humans seem to be evolving, possessing higher intelligence than a regular human. Of course, society reacts against them with fear. In a separate plot line explorers are using the gap world (where there is no earth present) to travel to Mars and explore stepwise Mars.
While Prachett and Baxter are talented writers, the whole long earth series has failed to engage and seems rather pointless and meandering. Once we get past the novelty of the stepwise universe, the number of alternate earths has grown so big as to be impossible to write about.