It's a colorful survey of life before the mass extinction event, based on extensive studies and the use of ever-improving technology. Halliday is careful to note that the contents of his book are “grounded in fact, either directly observable from the fossil record, strongly inferred, or, where our knowledge is incomplete, plausible based on what we can say for sure.” Otherlands is comprised of 16 chapters, each centered on a specific locale (Africa, Alaska, Chile, Antarctica, and elsewhere) and geologic era (Pleistocene, Cenozoic, Mesozoic, etc.).