Rating: Loved (Hated-Disliked-Okay-Liked-Loved)
(Edit: While the cover is what initially caught my attention and made me interested in the book, it's actually a pretty poor representation of the story. There are giant horses in it, and there are kacks (giant wolf-like things), but the wolves especially are just a very minor part.)
While I love both fantasy and sci-fi equally, for some reason I read very little sci-fi. Every time I read a sci-fi book, I always tell myself I need to read more of it. Child of Earth was no exception.
Set in the future, scientists have found not only that parallel worlds exist, but how to cross over to them. Each one is a version of Earth with some small change -- however, sometimes those small changes happened thousands or millions of years ago, so it could lead to very big changes. No moons, two moons, worlds where dinosaurs never died off, worlds with a totally different atmosphere: as many differences as you can imagine.
In addition, the gate technology that connects to those other worlds can sometimes by mistake (or on purpose) force a "time slip", so more time happens on the parallel world than on ours. This was useful for places they wanted to terraform. One character compared it to cooking: You add an ingredient, then let it simmer a while, then take a taste and add something else. You could get thousands of years of terraforming done in months or years.
The book centers around Kaer (a preteen girl) and her "extended" family getting ready to go to one of those worlds. (In the future, family has become something bigger than it is now: There tended to be "family groups" made up of a couple couples, or one husband/wife and many husbands/wives. Gender was very much fluid as well, people can and did decide to be male or female, then could change again if they wanted.)
The world they were training for, Linnean, was made up of mostly grasslands -- grass more than twice as tall as the tallest men. Because of the size of the grass and the lower gravity, the world was populated by megafauna.
The science end of things was wonderfully interesting, and David Gerrold is one of those authors whose world-building is so interesting that I would be 100% fine if the book had zero plot. Which is good, as "nothing happened" through the first 80% of the book. But the lack of things happening was no down-side at all! The book was so amazingly interesting, all the things these modern people had to learn about to live on the no-technology world of Linnean.
The plot/conflict came from the native human population on Linnean. Due to one of those time slips, some scientists/techs/explorers got trapped over there, and the gate couldn't be established for thousands of years -- long enough for them to have long since forgotten Earth ever existed.
Unfortunately the book does do the one thing I hate: Ends in the middle of the story. Seriously, it's like story for this trilogy was just cut into thirds with no attempt at all to make this book self-contained at all. I hate that so much. Luckily I have the second book already, and will be reading it next, but the third book isn't published yet and I can't see the second book ending any better.
Not only do I recommend Child of Earth, I intend to read many more things by him. I can't say everything he's written, because he's been a writer for a long, long time (he wrote the Trouble with Tribbles Star Trek ep!) and he's very prolific, but I'm fully intending to read a lot more of his work.