Abstract
Hydrothermal fields on the prebiotic Earth are candidate environments for biogenesis. We propose a model in which molecular systems driven by cycles of hydration and dehydration in such sites undergo chemical evolution in dehydrated films on mineral surfaces followed by encapsulation and combinatorial selection in a hydrated bulk phase. The dehydrated phase can consist of concentrated eutectic mixtures or multilamellar liquid crystalline matrices. Both conditions organize and concentrate potential monomers and thereby promote polymerization reactions that are driven by reduced water activity in the dehydrated phase. In the case of multilamellar lipid matrices, polymers that have been synthesized are captured in lipid vesicles upon rehydration to produce a variety of molecular systems. Each vesicle represents a protocell, an “experiment” in a natural version of combinatorial chemistry. Two kinds of selective processes can then occur. The first is a physical process in which relatively stable molecular systems will be preferentially selected. The second is a chemical process in which rare combinations of encapsulated polymers form systems capable of capturing energy and nutrients to undergo growth by catalyzed polymerization. Given continued cycling over extended time spans, such combinatorial processes will give rise to molecular systems having the fundamental properties of life.
Highlights
The scenario proposed here is based on specific properties of hydrothermal sites characteristic of volcanic regions on today’s Earth that we assume are analogues of similar sites on the prebiotic Earth.Two such sites have been proposed, one associated with submarine hydrothermal activity [1,2] and a second associated with volcanic land-masses emerging through a global ocean [3]
If biologically relevant compounds are detected in a meteorite, it is plausible that similar compounds could be synthesized by geochemical processes on the early Earth
It is important to note that the amphiphilic components of the system are not pure species, but, instead, include a variety of molecules capable of self-assembly into membranes. These are mixed with monomers and polymers that are not at equilibrium, but in a steady state in which hydrolysis is balanced by synthesis
Summary
The scenario proposed here is based on specific properties of hydrothermal sites characteristic of volcanic regions on today’s Earth that we assume are analogues of similar sites on the prebiotic Earth. The garbage bags grow and occasionally split in two, and the ones that grow and split fastest win” [4] This conjecture has been explored in the laboratory with systems of vesicles composed of fatty acids [5,6]. That the first forms of life continuously exchanged genetic information rather than existing as individual organisms This was recently summarized by Nigel Goldenfeld, who wrote: “Early life was much more collective, much more communal than it is today, the core cellular machinery such as translational machinery. It may well have been that there was massive endosymbiosis, meaning organisms were very porous and could crash into each other and absorb each other on a massive scale and that's how cellular functions were transmitted.” [9] Stuart Kauffman [10] has proposed a theoretical framework that provided us insight on how functional polymers can enable hill climbing through phase spaces of prebiotic evolution toward the origin of life
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