RETRACTED ARTICLE: Generation of long-chain fatty acids by hydrogen-driven bicarbonate reduction in ancient alkaline hydrothermal vents

Abstract

The origin of life required membrane-bound compartments to allow the separation and concentration of internal biochemistry from the external environment and establish energy-harnessing ion gradients. Long-chain amphiphilic molecules, such as fatty acids, appear strong candidates to have formed the first cell membranes although how they were first generated remains unclear. Here we show that the reaction of dissolved hydrogen and bicarbonate with the iron-rich mineral magnetite under conditions of continuous flow, alkaline pH and relatively low temperatures (90 °C) generate a range of functionalised long-chain aliphatic compounds, including mixed fatty acids up to 18 carbon atoms in length. Readily generated membrane-forming amphiphilic organic molecules in the first cellular life may have been driven by similar chemistry generated from the mixing of bicarbonate-rich water (equilibrated with a carbon dioxide-enriched atmosphere) with alkaline hydrogen-rich fluids fed by the serpentinisation of the Earth's iron-rich early crust.

Keywords: Biogeochemistry; Geochemistry; Mineralogy; Origin of life.

Fig. 1. Total Ion Chromatograms of magnetite following hydrothermal reaction compared to the controls.

A Comparison of a representative of one of the three replicate total ion chromatograms obtained from reacting magnetite with HCO₃⁻ and H₂ at 90 °C and 16 bar total pressure for 16 h alongside controls. (a) Organic molecules generated using magnetite with H₂ and HCO₃⁻. (b) Control sample using magnetite with H₂ (c) Control sample using quartz with H₂ and HCO₃⁻ (d) Control sample using quartz with H₂. B Magnification of the chromatogram region bounded by the broken line box in (A). Peaks with signal: noise ratio <5:1 or with a reverse match factor <65.0 to the NIST20 library are not labelled (Supplementary Data 3 for peak identities obtained from the NIST20 library).

Fig. 2. ATR-FTIR spectrum and enlarged regions of interest of magnetite following hydrothermal reaction at 90 °C and 16 bar total pressure for 16 h compared to the controls.

(a) Magnetite with H₂ and HCO₃⁻. (b) Control sample using magnetite with H₂ (c) Control sample using quartz with H₂ and HCO₃⁻ (d) Control sample using quartz with H₂. A A representative of three ATR-FTIR replicate spectra annotated with candidate functional groups. B Enlarged 3150 cm⁻¹ to 3000 cm⁻¹ region showing carbon-hydrogen bonding, and (C) Enlarged 2000 cm⁻¹–1600 cm⁻¹ region showing carbon-oxygen bonding, the identified peaks are annotated and highlighted by the shaded areas.

Fig. 3. TGA traces of the CO₂ and H₂O evolved from organic material of magnetite compared to controls following hydrothermal reaction at 90 °C and 16 bar total pressure for 16 h.

CO₂ (m/z 44) and H₂O (m/z 18) traces resulting from the thermal decomposition of organic material between 35 to 500 °C. (a) Magnetite with H₂ and HCO₃⁻. (b) Control sample using magnetite with H₂. (c) Control sample using quartz with H₂ and HCO₃⁻. (d) Control sample using quartz with H₂. Desorption = atmospheric water released from mineral surfaces; Carbonate = water produced from the combustion of hydrogen in the carbonate; vug = water escaping from vugs. Hydrocarbon = components consistent with the combustion of hydrogen in hydrocarbons; Aromatic = component consistent with the combustion of aromatics^,.

Fig. 4. TGA traces evolved from the magnetite surfaces following hydrothermal reaction using ¹³C NaHCO₃ and hydrogen.

(a) ¹³CO₂ (m/z 45), (b) ¹²CO₂ (m/z 44) and (c) H₂O (m/z 18). Desorption = atmospheric water released from mineral surfaces; Carbonate = water produced from the combustion of hydrogen in the carbonate; Hydrocarbon = components consistent with the combustion of hydrogen in hydrocarbons. Aromatic = component consistent with the combustion of aromatics^,.