Complicated stuff explained in simple words.
It's hard to decide how to classify Thing explainer. On the one hand it should be a children's book: I once owned a book called "What makes it go?" that did a similar job. And Monroe does an excellent job at explaining things that children will want to know about: the US space team's up-goer five, Earth's past, the Big thing tiny hitter, and more. And also some things they hopefully won't want to know too much about, like the Machine for burning cities.
But there's also something of a conceit to the book, in that it's limiting its vocabulary for effect and not simply for clarity of explanation. That makes some things a lot harder than they need to be, and marks the book out as really not for children at all.
That being said, it's extremely enjoyable, as well-written and well-illustrated as What If?: Serious Scientific Answers to Absurd Hypothetical Questions and the rest of xkcd. Definitely to be recommended.
Finished on Sun, 28 Feb 2016 10:16:56 -0800. Rating 4/5.