Ingredients for life found in 3.5 billion-year-old fluid inclusions from Pilbara Craton, Western Australia.
Primeval Microbes likely required small organic molecules to act as building blocks for biomass and as catabolic substrates for heterotrophic metabolism. A potential source of such compounds includes recycled and redistributed organic matter from pre-existing biomass. In addition, ample exogenous organic matter probably had been delivered to the early Earth by interplanetary dust particles and meteorites. Experiments have also shown that organic molecules relevant for primordial life can be formed by synthesising organic compounds from inorganic atmospheric gases. As important, endogenous synthesis and processing of organic molecules could have occurred in marine and terrestrial (i.e. hot spring) hydrothermal environments. In such settings, organic molecules may form, or react, at elevated temperatures and pressures within the steady flow of inorganic hydrothermal chemistry (e.g. hydrogen sulphide, carbon dioxide, molecular hydrogen). One hypothesis on organic synthesis at hydrothermal sites suggests that the reaction of iron(II) sulphide to pyrite with hydrogen sulphide drives the reduction of carbon dioxide to organic molecules. Moreover, a primordial carbon fixation mechanism involving the reaction of carbon monoxide with methanethiol on catalytic metal (nickel or iron) sulphide surfaces could be demonstrated in the laboratory under hydrothermal conditions. This experiment produced an activated form of acetic acid that represents a plausible building block for further organic synthesis, for example, into acyl lipids. As yet, however, such distinctive organic molecules have not been found in rocks that directly testify to the emergence of life on our planet.