Green Rust: The Simple Organizing ‘Seed’ of All Life?

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.

Microfluidic Production of Pyrophosphate Catalyzed by Mineral Membranes with Steep pH Gradients

“…Accordingly, we could readily synthesize membranes of highly oxygen sensitive iron(II, III) hydroxides by co‐precipitation of Fe 2+ and Fe 3+ along the solution interface of our microfluidic device. This is significant for origin of life chemistry since green rust (among other iron oxyhydroxides) is proposed to have existed in alkaline hydrothermal vents on the early Earth, forming inorganic membranes transected by pH and other gradients, and may have been capable of driving prebiotic redox and phosphorus chemistry . In this experiment, the alkaline solution contained 0.5 m NaOH, whereas the acidic iron solution contained 0.33 m Fe 2+ and 0.17 m Fe 3+ .…”

“…Steep disequilibria across mineral membranes are thought to be significant for the emergence of metabolism in an alkaline vent setting, and since disequilibria‐converting engines linked to ATP/ADP or PP i hydrolysis are essential for life, it has been suggested that analogous processes–though mineral‐driven–may have been involved in the emergence of metabolism . Particularly the mineral green rust, a mixed valence iron oxyhydroxide, has been proposed to serve various prebiotic functions as an engine, electron transfer agent, and catalyst for organic synthesis . A major challenge for origins‐of‐life studies, particularly in such complex geochemical systems as vents, is the vastness of the search space that involves both physical and chemical factors such as temperature gradients, catalytic materials, porosities, and concentrations.…”

Origin of Life’s Building Blocks in Carbon- and Nitrogen-Rich Surface Hydrothermal Vents

“…This indicates that protocellular life at hydrothermal vents must have come equipped with proteins, RNA and cell membranes, which in turn makes amino acids, nucleotides and vesicles minimal prerequisites for hydrothermal vent origin of life scenarios. However, at present, photochemically driven cyanosulfidic and cyanosulfitic protometabolism is the only path to forming all of these prerequisites in one environment, and this protometabolism proceeds only at surfaces exposed to sunlight.An alternative point of view is that both the prebiotic chemistry and subsequent evolution occurred in underwater alkaline hydrothermal vents [7,11,12]. Recently, this hypothesis has gained support from the detection of nanomolar concentrations of amino acids of possible abiotic origin, found in the oceanic lithosphere proximal to underwater hydrothermal environments [13].…”

“…An alternative point of view is that both the prebiotic chemistry and subsequent evolution occurred in underwater alkaline hydrothermal vents [7,11,12]. Recently, this hypothesis has gained support from the detection of nanomolar concentrations of amino acids of possible abiotic origin, found in the oceanic lithosphere proximal to underwater hydrothermal environments [13].…”

The Emergence of Life

“…It was suggested that redox reactions between precipitated transition metal sulfides, such as iron monosulfide (FeS), could have provided the free energy and electrons for prebiotic synthesis through the generation of pyrite (Wächtershäuser 1988). Another approach also involving FeS and ferrous-ferric oxyhydroxide, but in the form of a putative membrane separating alkaline sulfide-bearing hydrothermal fluids from acidulous Fe-bearing ocean, had the effect of imposing both a redox and a pH gradient with a total potential approaching 1 V, sufficient theoretically to drive the reduction of carbon dioxide (Russell andHall 1997, 2006). These gradients are, and were, sustainable for at least 100,000 years (Ludwig et al 2011).…”