On the why's and how's of clay minerals' importance in life's emergence

Abstract

A possibly prominent role for Green Rust minerals in life's emergence is inferred from a comparison of their structural, mechano-dynamic and electrochemical properties and of the layout of bioenergetic, i.e. free energy converting processes in extant organisms. From fundamental thermodynamic considerations, the conversion of environmental free energy into the decrease of entropy that defines life is an indispensable ingredient for life to emerge. A specific scenario for life's emergence mediated by Green Rust minerals in the framework of the alkaline hydrothermal vent hypothesis is proposed.

Six ‘Must-Have’ Minerals for Life’s Emergence: Olivine, Pyrrhotite, Bridgmanite, Serpentine, Fougerite and Mackinawite

“…For example, haven’t clays been at the forefront of minerobiolization hypotheses and experiments since Bernal [ 148 , 192 ]? But green rust/fougerite is a clay [ 151 ] and of the other likely vent precipitates—hisingerite (Fe 3+ 2 Si 2 O 5 [OH] 4 ·2H 2 O), greenalite (~[Fe 2+ ,Fe 3+ ] 2 3[Si 2 O 5 ][OH] 4 ), accompanied by amorphous silica—fougerite is the prime candidate [ 49 , 59 , 146 , 152 ]. It has that distinction owing to its variable valence sites, its propensity to juggle electrons and protons in and out of its extensive reactive and flexible internal surfaces, and its proven worth as an abiotic nitrate/nitrite reductase, aminase and generator of hydrogen fuel from water [ 146 , 156 , 158 , 218 , 219 ].…”

“…The green rust mineral fougerite is a mixed-valence redox-flexible semi-conducting naturally-occurring anionic clay, dosed with Mg 2+ , Ni 2+ , Mn 2+ , and Co 2+ [ 146 , 147 ]. Fougerite’s extensive inner surfaces appear to provide the ‘mechanistic’ potential to fill the roles of the redox- and pH-converter that enabled life’s emergence by driving endergonic—thermodynamically uphill—processes [ 41 , 43 , 62 , 130 , 145 , 148 , 149 , 150 , 151 ]. And there was certainly no want for fougerite in the all-enveloping early ocean—the mineral precursor to the diagenetic magnetite comprising the first known banded iron formation outcropping in western Greenland [ 45 , 59 , 60 , 152 , 153 , 154 ].…”

“…Yet to be tested are (i) the presumed potential of green rust situated in the membrane to also act as a proton wire, a proton pyrophosphatase, methane monooxygenase, polymerase and (ii) as an engine of synthesis in the production of aromatic rings (cf. quinones and flavins) [ 62 , 65 , 130 , 145 , 150 , 151 , 160 , 161 , 162 ].…”

“… Cross-section of two individual iron oxyhydroxide layers of the double layered mineral fougerite. In the AVT fougerite nano- to micro-crystals comprise the mid and outer portions of an inorganic membrane (see Figure 5 ) precipitated by—but separating the acidulous ocean from—the alkaline hydrothermal spring waters [ 145 , 150 , 151 ]. The detailed structure shows the contrasting heights of the interstitial space (the interlayer) between two layers of a redox-flexible fougerite nanocrystal (e.g., Fe 2+ 4 Fe 3+ 2 [OH] 12 ·CO 3 ·3H 2 O ⇔ Fe 2+ 2 Fe 3+ 4 O 2 [OH] 10 ·CO 3 ·3H 2 O) ( Figure 5 ).…”

The “Water Problem”(sic), the Illusory Pond and Life’s Submarine Emergence—A Review

“…The nanochemistry and nanotechnology literature appears to have passed these complainants by! In AVT’s defense redox catalysis and polymerization can be promoted within nanometer-sized pores and interlayers such as to be found in layered double hydroxides, including fougerite (~green rust), silica films, amyloid and peptide nests [ 72 , 193 , 194 , 195 , 196 , 197 , 198 , 199 , 200 , 201 , 202 , 203 , 204 , 205 , 206 , 207 , 208 , 209 , 210 , 211 , 212 , 213 , 214 , 215 , 216 ]. Moreover, it should be recalled that the AVT is the only theory which proposes a viable and explicit mechanism for the generation of out-of-equilibrium pyrophosphates as we will address in the next section.…”