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Over the past half century of serious research on the origin of life, several schools of thought have emerged that focus on “worlds” and what came first in the pathway to the origin of life. One example is the RNA World, a term coined by Walter Gilbert after the discovery of ribozymes. Other examples include the Iron-Sulfur World of Günther Wächtershäuser and the Lipid World proposed by Doron Lancet and coworkers. Then we have a competition between “metabolism first” and “replication first” schools. The worlds and schools have the positive effect of sharpening arguments and forcing us to think carefully, but they also can lock researchers into defending their individual approaches rather than looking for patterns in a larger perspective. One of the main themes of this book is the notion that the first living cells were systems of functional polymers working together within membranous compartments. Therefore, it is best not to think of “worlds” and “firsts” as fundamentals but instead as components evolving together toward the assembly of an encapsulated system of functional polymers. At first the polymers will be composed of random sequences of their monomers, and the compartments will contain random assortments of polymers. Here, we refer to these structures as protocells which are being produced in vast numbers as they form and decompose in continuous cycles driven by a variety of impinging, free-energy sources. This chapter describes how thermodynamic principles can be used to test the feasibility of a proposed mechanism by which random polymers can be synthesized. There is a current consensus that early life may have passed through a phase in which RNA served as a ribozyme catalyst, as a replicating system, and as a means for storing and expressing genetic information. For this reason, we will use RNA as a model polymer, but condensation reactions also produce peptide bonds and oligopeptides. At some point in the evolutionary steps leading to life, peptides and RNA formed complexes with novel functional properties beyond those of the individual molecular species.

Alexander Ivanovich Oparin was first to consider the origin of life in strictly scientific terms. Oparin published The Origin of Life in 1924, in his native Russian language, and was active in the field for the next 50 years. During my initial field work in the volcanic regions of Kamchatka, organized with Vladimir Kompanichenko, we visited the Institute of Volcanology and Seismology in Petropavlovsk, and I happened to see the above quote painted on a wall near the entrance. Oparin’s proposal about how life can begin was intuitive because he had no experimental evidence as a foundation, but as our party rode in helicopters up and down the peninsula from one volcanic site to the next, I began to share his intuition. The focus of this chapter concerns the properties of water in contact with mineral surfaces heated by volcanism, inspired by what we saw in Kamchatka. Four billion years ago, as the global temperature decreased following the condensation of the ocean, there came a point at which the components required for the origin of life could assemble into systems of encapsulated polymers. Two alternative hydrothermal conditions have been proposed as sites where this could have occurred: salty seawater at submarine hydrothermal vents and freshwater circulating in hydrothermal fields associated with volcanic land masses. To weigh the alternatives, this chapter considers the chemical and physical properties of hydrothermal vents and hydrothermal fields and how each could contribute to the origin of cellular life. Questions to be addressed: What are the chemical and physical properties of hydrothermal vents? How do the properties of hydrothermal fields differ from those of vents? How are these properties related to the way that organic solutes can undergo physical and chemical interactions related to the origin of life? Suppose that an organic chemist decides to synthesize a new compound that involves making an ester bond. The chemist is provided with a solution of the two reactants such as acetic acid and ethanol, and then is given a choice: should the reaction be run in an ice bath or instead heated to boiling and refluxed?

Polyphosphazenes comprise by far the largest class of inorganic macromolecules. At least 700 different polymers of this type have been synthesized, with a range of physical and chemical properties that rivals that known hitherto only for synthetic organic macromolecules. Most polyphosphazenes have the general molecular structure. The polymer backbone consists of alternating phosphorus and nitrogen atoms, with two side groups, R, being attached to each phosphorus. The side groups may be organic, organometallic, or inorganic units. Each macromolecule typically contains from 100 to 15,000 or more repeating units linked end to end, which means that (depending on the organic side groups) the highest molecular weights are in the range of 2 million to 10 million. The bonding structure in the backbone is formally represented as a series of alternating single and double bonds. However, this formulation is misleading. Structural measurements suggest that all the bonds along the chain are equal or nearly equal in length, but without the extensive conjugation found in organic polyunsaturated materials. This anomaly will be discussed later. In addition to linear polyphosphazenes with one type of side group, other molecular architectures have also been assembled. These include polyphosphazenes in which two or more different side groups, R1 and R2, are arrayed along the chain in random, regular, or block distributions. Other species exist with short phosphazene branches linked to phosphorus atoms in the main chain. Also available are macromolecules in which carbon or sulfur replace some of the phosphorus atoms in the skeleton. Star-geometry structures, using the symbolism defined, are also accessible. A new and growing area is the field of phosphazene-organic and phosphazene-polysiloxane hybrid linear copolymers, and comb copolymers of the types. In addition, polymers are known in which six-membered phosphazene rings are side groups linked to organic polymers, and where phosphazene rings are linked by organic connector groups to form cyclolinear or cyclomatrix materials.