Greenalite Nanoparticles in Alkaline Vent Plumes as Templates for the Origin of Life

Abstract

Mineral templates are thought to have played keys roles in the emergence of life. Drawing on recent findings from 3.45-2.45 billion-year-old iron-rich hydrothermal sedimentary rocks, we hypothesize that greenalite (Fe₃Si₂O₅(OH)₄) was a readily available mineral in hydrothermal environments, where it may have acted as a template and catalyst in polymerization, vesicle formation and encapsulation, and protocell replication. We argue that venting of dissolved Fe²⁺ and SiO₂(aq) into the anoxic Hadean ocean favored the precipitation of nanometer-sized particles of greenalite in hydrothermal plumes, producing a continuous flow of free-floating clay templates that traversed the ocean. The mixing of acidic, metal-bearing hydrothermal plumes from volcanic ridge systems with more alkaline, organic-bearing plumes generated by serpentinization of ultramafic rocks brought together essential building blocks for life in solutions conducive to greenalite precipitation. We suggest that the extreme disorder in the greenalite crystal lattice, producing structural modulations resembling parallel corrugations (∼22 Å wide) on particle edges, promoted the assembly and alignment of linear RNA-type molecules (∼20 Å diameter). In alkaline solutions, greenalite nanoparticles could have accelerated the growth of membrane vesicles, while their encapsulation allowed RNA-type molecules to continue to form on the mineral templates, potentially enhancing the growth and division of primitive cell membranes. Once self-replicating RNA evolved, the mineral template became redundant, and protocells were free to replicate and roam the ocean realm.

Keywords: Alkaline vents; Clay templates; Greenalite; Hydrothermal sediments; Origin of life; RNA.

FIG. 1.

Major geological and biological events during the first 2 billion years of Earth's history. Greenalite nanoparticles preserved in marine sedimentary cherts from 3.45- to 2.45-billion-year-old banded iron formations (BIFs). LHB = Late heavy bombardment; GOE = Great Oxidation Event. (1) 3.45 Ga Marble Bar Chert, Western Australia; (2) 3.20 Ga Gorge Creek Group; (3) 3.10 Ga Nimingarra Iron Formation; (4) 2.75 Ga Weld Range iron formation; (5) 2.63 Ga Jeerinah Formation; (6) 2.60 Ga Marra Mamba Iron Formation; (7) 2.56 Ga Wittenoom Formation; (8) 2.55 Ga Mt Sylvia Formation; (9) 2.50 Ga Mt McRae Shale; (10) 2.50–2.45 Ga Brockman Iron Formation. Color images are available online.

FIG. 2.

(A) Polished thin section of finely laminated, greenalite-rich chert. (B) Plane polarized light image of laminated, greenalite-rich chert. (C) Transmission electron microscope (TEM) bright-field image showing randomly oriented greenalite nanoparticles “floating” in chert cement. (D) TEM bright-field image of greenalite nanoparticles (inset 2C). (E, F) High-resolution (lattice fringe) TEM images of greenalite nanoparticles showing the spacing and direction of the (001) planes. Color images are available online.

FIG. 3.

(A, B) High-resolution (lattice fringe) TEM images of a greenalite particle showing the spacing (7.0–7.2 Å) and direction of the (001) planes and the spacing (∼22 Å) and direction of the characteristic modulated structure.

FIG. 4.

Diagram showing mixing of acidic and alkaline hydrothermal plumes in the Hadean ocean. (1) The emission of alkaline, carbon- and hydrogen-rich vent fluids into water column above serpentinizing ultramafic rocks (e.g., komatiitic lavas). (2) Emission of black smoker vent plumes, enriched in metals, greenalite, and nutrients relative to seawater. (3) Mixing of acidic vent plumes with local alkaline vent plumes, bringing together the chemicals leached from mafic and ultramafic rocks. The rise in alkalinity of metal-rich plumes triggered the rapid nucleation and precipitation of greenalite nanoparticles, which catalyzed the assembly of primitive vesicles and synthesis of RNA-based genetic polymers. Color images are available online.

FIG. 5.

Diagram of the approximate crystal structure of greenalite along its b-axis (modified after Guggenheim and Eggleton, ; Capitani et al., 2009). Color images are available online.

FIG. 6.

(A) Diagram depicting greenalite nanoparticles encapsulated within membranous vesicles composed of amphiphilic compounds. (B) Postulated adsorption and assembly of RNA-type oligomers (∼20 Å wide) along modulated structures (∼22 Å wide) on the edges of greenalite particles (see Fig. 3). Color images are available online.

FIG. 7.

Diagram showing hypothetical scenarios for the assembly of nucleotides by adsorption of phosphate groups onto metal cations (e.g., Mg²⁺, Fe²⁺) regularly spaced in the linear corrugations along the edges of greenalite nanoparticles. In this scenario, mineral surfaces may have catalyzed the assembly of a cocktail of short and long chains of organic molecules including single- and double-stranded RNA-type genetic polymers. Episodic desorption released the organic compounds from the surface adsorption sites. Color images are available online.

FIG. 8.

Potential environments where greenalite templates may have promoted polymerization and vesicle assembly. Scenario 1: mixing of hot, acidic, metal-rich plumes with organic-rich alkaline plumes. Scenario 2: suspended greenalite nanoparticles in submarine hydrothermal plumes mix with biochemical compounds discharged from terrestrial springs. Scenario 3: terrestrially generated greenalite and biochemical compounds combine in hot springs and pools. Color images are available online.