Chapter 1, Introduction, has three parts. The first provides an historical overview of the main theories and myths that dominated people’s minds, from antiquity to the modern era, regarding the emergence of life. The second part introduces the concept of life as a physical-chemical phenomenon, which is then used in the third part to describe the commonly accepted theory of abiogenesis, which holds that life could emerge spontaneously on our planet via chemical reaction between common simple molecules, through more complex ones.
Chapter 2 provides a summary of the main aspects of life on Earth. The first part describes aspects that differ between organisms, and which contribute to their vast diversity. The second and third parts focus on the three key aspects that are shared by all known organisms: chemical, molecular, and cellular. The fourth part discusses viruses, which includes only some of the shared aspects, and the last part uses all of the above to propose a definition of life which is more accurate than the one often used.
Chapter 3 elaborates on the theory of abiogenesis, which is currently the widely accepted notion of how life emerged on Earth. It starts by discussing the question of when have life first appeared on Earth. This is done by reviewing various evidence of the geology and geochemistry of ancient Earth, as well as fossil and chemical evidence of putative primordial organisms that existed at that time. The discussion then proceeds to abiogenesis; it reviews the key evidence and scientific studies carried out so far in an attempt to understand how spontaneous chemical reactions between simple molecules could have led to the appearance of more complex molecules, then to biomolecules, and finally to the emergence of the first living cells. The last part of the chapter discusses the implications of abiogenesis to the spontaneous emergence of life on other planets as well, and which planets or moons in our own solar system are most likely to harbor simple living organisms.
Chapter 4 discusses the evolution of proteins, a process that served as a basis for the evolution of all living organisms on Earth. The process is discussed on the chemical, structural, and functional levels; it starts with the putative chemical reactions that converted simple peptides to small proteins, and continues to the genetic processes that allowed the small proteins to keep evolving into highly complex and functional biomolecules.