Abstract
Korenaga and coworkers presented evidence to suggest that the Earth’s mantle was dry and water filled the ocean to twice its present volume 4.3 billion years ago. Carbon dioxide was constantly exhaled during the mafic to ultramafic volcanic activity associated with magmatic plumes that produced the thick, dense, and relatively stable oceanic crust. In that setting, two distinct and major types of sub-marine hydrothermal vents were active: ~400 °C acidic springs, whose effluents bore vast quantities of iron into the ocean, and ~120 °C, highly alkaline, and reduced vents exhaling from the cooler, serpentinizing crust some distance from the heads of the plumes. When encountering the alkaline effluents, the iron from the plume head vents precipitated out, forming mounds likely surrounded by voluminous exhalative deposits similar to the banded iron formations known from the Archean. These mounds and the surrounding sediments, comprised micro or nano-crysts of the variable valence FeII/FeIII oxyhydroxide known as green rust. The precipitation of green rust, along with subsidiary iron sulfides and minor concentrations of nickel, cobalt, and molybdenum in the environment at the alkaline springs, may have established both the key bio-syntonic disequilibria and the means to properly make use of them—the elements needed to effect the essential inanimate-to-animate transitions that launched life. Specifically, in the submarine alkaline vent model for the emergence of life, it is first suggested that the redox-flexible green rust micro- and nano-crysts spontaneously precipitated to form barriers to the complete mixing of carbonic ocean and alkaline hydrothermal fluids. These barriers created and maintained steep ionic disequilibria. Second, the hydrous interlayers of green rust acted as engines that were powered by those ionic disequilibria and drove essential endergonic reactions. There, aided by sulfides and trace elements acting as catalytic promoters and electron transfer agents, nitrate could be reduced to ammonia and carbon dioxide to formate, while methane may have been oxidized to methyl and formyl groups. Acetate and higher carboxylic acids could then have been produced from these C1 molecules and aminated to amino acids, and thence oligomerized to offer peptide nests to phosphate and iron sulfides, and secreted to form primitive amyloid-bounded structures, leading conceivably to protocells.
Highlights
Chemistry unbridled could not have led to life [1,2,3,4]
What were the materials and what was the environment that could have allowed these gradients to be used to drive the key endergonic processes needed to launch life? In our original alkaline hydrothermal vent (AHV) model, we suggested that life emerged at an alkaline hydrothermal spring on meeting the carbonic Hadean
We list experiments favoring the theory overlooked by, for example, Ritson and his coworkers, but detail further predictions, some of which could be falsified, reveal embarrassing missing links, or even leave the AHVT as just one more casualty of the general theory of natural rejection (Table 1) [296,297]! In Feynman’s exacting dictum, here, “we are trying to prove ourselves wrong as quickly as possible, because only in that way can we find progress” [298]. The purpose of this contribution was to suggest how the submarine alkaline hydrothermal vent model could be subjected to stringent tests that would indicate its failure, or partial failure, to provide a path forward in emergence-of-life research
Summary
Chemistry unbridled could not have led to life [1,2,3,4]. Redox and pH gradients were required together with ‘engines of disequilibria conversion’ to allow these gradients to do the work of. Along with the subordinate iron sulfide mackinawite ([Fe>Ni]S) are proposed to have functioned as electrochemical nano-engines acting to convert the imposed external proton and redox disequilibria into the internal disequilibria necessary to bring life into being [4,7] These engines might effect free energy conversions of various types driven by Brownian motion with built-in escapement mechanisms that prevent back reactions [3,4,14]. The contribution of this study is suggesting how green rust (~[Fe2+ 6x Fe3+ 6(1−x) O12 H2(7−3x) ]2+ ·[CO2− 3 ·3H2 O]2− ), nickel-rich mackinawite ([Fe>Ni]S), greigite (Fe5 NiS8 ), violarite (Fe2 Ni4 S8 ), and possibly tochilinite (FeS[Mg,Fe2+ ][OH]2 ) precipitated as the first response to the alkaline vent-versus-ocean interfacing, may have been co-opted, adapted, and systematized as nano-engines and catalysts at a Hadean submarine alkaline mound, enabling the emergence of life [4,16]. With these assumptions in mind, we suggest a testable model whereby the first and simplest pathways and enzymatic mechanisms are assumed to reflect on early beginnings and availabilities of disequilibria, mechanisms for their conversion, as well as on the trace metals and phosphate that contributed to these processes both and
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