Formed around 4.6 billion years ago from the debris of the Big Bang and long-dead stars, the Earth was at first nothing special, but somehow it evolved to become the most amazing place in the known universe. The only living planet we know of, it also has a very unusual moon, a remarkably dynamic surface, a complex atmosphere, and a mysterious interior. Written by biologists, seismologists, and meteorologists, the essays here explore how it is that despite centuries of research, only now are we starting to understand Earth's complexity.