Foreword -- Preface -- Introductory -- What is Gaia? -- Exploring Daisyworld -- The Archean -- The middle ages -- Modern times -- The contemporary environment -- The second home -- God and Gaia -- Gaia since 1988 -- Epilog -- References -- Further Reading -- Index.

This paper compares two approaches that attempt to explain the origin of life, or biogenesis. The more established approach is one based on chemical principles, whereas a new, yet not widely known approach begins from a physical perspective. According to the first approach, life would have begun with—often organic—compounds. After having developed to a certain level of complexity and mutual dependence within a non-compartmentalised organic soup, they would have assembled into a functioning cell. In contrast, the second, physical type of (...) approach has life developing within tiny compartments from the beginning. It emphasises the importance of redox reactions between inorganic elements and compounds found on two sides of a compartmental boundary. Without this boundary, “ life ” would not have begun, nor have been maintained; this boundary—and the complex cell membrane that evolved from it—forms the essence of life. (shrink)

Life appears to be a natural property of matter, but the problem of its origin only arose after early scientists refuted continuous spontaneous generation. There is no chance of life arising ‘all at once’, we need the standard scientific incremental explanation with large numbers of small steps, an approach used in both physical and evolutionary sciences. The necessity for considering both theoretical and experimental approaches is emphasized. After describing basic principles that are available (including the Darwin-Eigen cycle), the search for (...) origins is considered under four main themes. These are the RNA-world hypothesis; potential intermediates between an RNA-world and a modern world via the evolution of protein synthesis and then of DNA; possible alternatives to an RNA-world; and finally the earliest stages from the simple prebiotic systems to RNA. The triplicase/proto-ribosome theory for the origin of the ribosome is discussed where triples of nucleotides are added to a replicating RNA, with the origin of a triplet code well-before protein synthesis begins. The length of the code is suggested to arise from the early development of a ratchet mechanism that overcomes the problem of continued processivity of an RNA-based RNA-polymerase. It is probable that there were precursor stages to RNA with simpler sugars, or just two nucleotides, but we do not yet know of any better alternatives to RNA that were likely to arise naturally. For prebiotic stages (before RNA) a flow-reactor model is suggested to solve metabolism, energy gradients, and compartmentation simultaneously – thus the intense interest in some form of flow reactor. If an autocatalytic cycle could arise in such a system we would be major steps ahead. The most likely physical conditions for the origin of life require further clarification and it is still unclear whether the origin of life is more of an entropy (information) problem (and therefore high temperatures would be detrimental), rather than a kinetic problem (where high temperatures may be advantageous). (shrink)