One of the leading theories regarding the origin of life on Earth is its emergence in hot springs at the bottom of the ocean. At the same time, the initial role in providing organisms with energy is assigned to chemical reactions with iron sulfide.
Iron sulfides and their role in prebiotic reactions
An international team of scientists has published a study covering the potential role of iron sulfides in the formation of life in early Earth’s hot springs. According to the researchers, the sulfides could catalyze the reduction of gaseous carbon dioxide to prebiotic organic molecules in a non-enzymatic way.
The work, published in Nature Communications, offers new insights into Earth’s early carbon cycles and prebiotic chemical reactions, emphasizing the importance of iron sulfides in supporting the hypothesis of the origin of life from hot springs on Earth.
Iron sulfides, common in hydrothermal systems of the early Earth, may have contributed to basic prebiotic chemical reactions, similar to the function of cofactors in modern metabolic systems. Previous studies of iron sulfides and the origin of life have focused primarily on deep-sea alkaline hydrothermal vents that provide favorable conditions such as high temperature, pressure, pH gradients, and hydrogen (H2) from serpentinization, factors assumed to support prebiotic carbon fixation.
However, some scientists have suggested that terrestrial hot springs should be considered as another likely site for the origin of life due to their rich mineral content, diverse chemicals, and abundant sunlight.
Catalytic activity of iron sulfides
To investigate the role of iron sulfides in terrestrial prebiotic carbon fixation, the research team synthesized a series of nanoscale iron sulfides from mackinawite, including pure iron sulfide and iron sulfides doped with common hot spring elements such as manganese, nickel, titanium, and cobalt.
Experiments have shown that these iron sulfides can catalyze the reduction of CO2 by H2 at certain temperatures (80-120 °C) and atmospheric pressure. Gas chromatography was used to quantify methanol formation.
The study confirmed that manganese-doped iron sulfides show extremely high catalytic activity at 120°C. This activity was further increased under UV (300-720 nm) and UV-enhanced (200-600 nm) light, indicating that sunlight may play a role in this reaction by facilitating chemical processes. In addition, the introduction of water vapor increased catalytic activity, further confirming that terrestrial vapor-filled hot springs may have served as key sites for non-enzymatic organic synthesis on the early Earth.
To further investigate the mechanism of CO2 reduction by H2, the team conducted in situ studies using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).
Efficiency of reactions with iron sulfide in hot springs
The results indicated that the reaction probably proceeds via a reverse water-gas shift (RWGS) process in which CO2 is first reduced to carbon monoxide (CO), which is subsequently hydrogenated to form methanol.
Density functional theory (DFT) calculations provided additional information, showing that manganese doping not only reduced the activation energy of the reaction, but also created highly efficient electron transfer centers, thereby increasing the reaction efficiency. The redox characteristics of iron sulfides make them functionally analogous to modern metabolic enzymes, providing a chemical basis for prebiotic carbon fixation.
This study stresses the potential for iron sulfides to catalyze prebiotic carbon fixation in early terrestrial hot springs, providing new directions for studying the origin of life and supporting efforts to search for extraterrestrial life.
Provided by phys.org
