Although the focus of this book is on the evolution of animals, no account of such evolution would be complete without a brief look at what happened before the first-ever animal evolved from something else. What was that something? How did it evolve, and from what? How far do we have to trace evolution back until we get to the origin of life? And, before that, what processes led from an uninhabitable Earth to one on whose surface life could begin? Finally, going back even further in time, how did planet Earth come into being in the context of the evolution of the Universe?

These are big questions indeed. In science, what we perceive as the biggest questions are usually the most exciting ones, but often also the hardest to answer. Luckily, much has been learned over the last century or so in relation to some of the ancient pre-animal events referred to above – but not all of them, as we will see.