The two major questions posed by this chapter are: What is life and how do we define and identify it? How did life originate? It discusses different definitions of life and the role of entropy as a constraint. It discusses some forms that may or may not meet differing definitions of life (e.g. prions, viruses). The various hypotheses, studies, and discoveries pertaining to the origins of life are explored, including the Miller–Urey experiment, the Murcheson meteorite, and more recent NASA experiments relating to the potential origins of DNA and complex proteins. It also discusses the conditions on Earth during the origins of life, and presents the current hypotheses for the origins of water on this planet. It also reviews the candidates for the earliest life on Earth discovered in the fossil record, and explores just how we would identify the oldest life.