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

Abstract

Life cannot emerge on a planet or moon without the appropriate electrochemical disequilibria and the minerals that mediate energy-dissipative processes. Here, it is argued that four minerals, olivine ([Mg>Fe]2SiO4), bridgmanite ([Mg,Fe]SiO3), serpentine ([Mg,Fe,]2-3Si2O5[OH)]4), and pyrrhotite (Fe(1−x)S), are an essential requirement in planetary bodies to produce such disequilibria and, thereby, life. Yet only two minerals, fougerite ([Fe2+6xFe3+6(x−1)O12H2(7−3x)]2+·[(CO2−)·3H2O]2−) and mackinawite (Fe[Ni]S), are vital—comprising precipitate membranes—as initial “free energy” conductors and converters of such disequilibria, i.e., as the initiators of a CO2-reducing metabolism. The fact that wet and rocky bodies in the solar system much smaller than Earth or Venus do not reach the internal pressure (≥23 GPa) requirements in their mantles sufficient for producing bridgmanite and, therefore, are too reduced to stabilize and emit CO2—the staple of life—may explain the apparent absence or negligible concentrations of that gas on these bodies, and thereby serves as a constraint in the search for extraterrestrial life. The astrobiological challenge then is to search for worlds that (i) are large enough to generate internal pressures such as to produce bridgmanite or (ii) boast electron acceptors, including imported CO2, from extraterrestrial sources in their hydrospheres.

Experimental Approaches for Testing the Hypothesis of the Emergence of Life at Submarine Alkaline Vents

“…Among them are minerals such as mackinawite (FeS) and its Ni-containing form, greigite (Fe 3 S 4 ) and violarite (FeNi 2 S 4 ). Some of these are considered key minerals [ 130 ] for the AHV and geoelectrochemistry models for the emergence of life. The CO 2 reduction electrocatalysis of the minerals is the most common reaction that was investigated.…”

“…The properties and environmental utility of this mineral are already known, even though they are not related to CO 2 reduction [ 133 , 134 ]. Besides its importance—once already mentioned for the AHV model, which considers it a key mineral for the emergence of life [ 130 ]—there has been little exploration of its electrochemistry in experiments applying in the AHV model. Evidence has shown that mackinawite interacts with CO and CO 2 under pH 6.8 conditions at room temperature [ 135 ].…”

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

“…UV has also been heralded as an energy source to free-up an electron from tricyanocuprate Cu(CN) 3 though again, exactly how the latter is produced in sufficient quantities, or at all, is also not demonstrated [ 60 ]. The Earth’s volatisphere was simply too oxidized to support a substantial source of that poison [ 61 , 62 , 63 ].…”

“…The reasoning goes that as the olivine-rich mantle is subjected to pressures beyond ~21 GPa in the lower mantle, it tends to metamorphose to perovskite, a mineral that requires a 3 + valence metal, normally aluminum. However, as the concentrations of Al 3+ in the mantle are too low to meet this entire need, iron in the olivine disproportionates, with Fe 3+ deputizing for the lacking Al 3+ , while the native iron Fe 0 tends to gravitate to the core [ 61 , 62 , 63 , 85 ]. The result is a relatively oxidized volatisphere comprising CO 2 > H 2 O >> N 2 [ 85 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 ].…”

Where Did Life Begin? Testing Ideas in Prebiotic Analogue Conditions

“…Hazen et al [ 2 ] pointed out that clay minerals have evolved over time, and there is little doubt that the Great Oxidation Event changed the composition of clays and other minerals exposed to molecular oxygen. Russell and Ponce [ 3 ] proposed a set of ‘must have’ minerals related to life’s origin in hydrothermal vent conditions, but it is uncertain whether these were available on the prebiotic Earth. On the other hand, parameters such as temperature, evaporation, pH, dissolved salts and concentration of organic solutes are variables in today’s hot springs and are likely to be analogous to the same variables four billion years ago.…”