Researchers have discovered organic molecules trapped in incredibly old rock formations in Australia, revealing what they say is the first detailed evidence of early chemical ingredients that could have supported Earth’s primary microbial life forms.
The discovery, made in the 3.5 billion-year-old Dresser Band in Pilbara Craton, Western Australia, adds to a significant body of research indicating ancient life in this part of the world – which is one of two deposits. smooth and exposed of the Earth on Earth dating from the Arch of Aeon.
In recent years, the Dresser’s formation’s hydrothermal rock has given repeated signals about what appears to be the oldest known life on land, with scientists discovering “definitive evidence” of microbial biosignatures dating back 3.5 billion years.
Now, in a new study, researchers in Germany have identified traces of specific chemistry that could have allowed the existence of such primordial organisms, finding biologically relevant organic molecules contained in the deposits of barite, a mineral formed by various processes. , including hydrothermal phenomena.
“In the field, barites are directly associated with fossilized microbial mats and smell like rotten eggs when freshly scratched,” explains geobiologist Helge Mißbach of the University of Cologne in Germany.
“Thus, I suspected that they contained organic materials that could have served as nutrients for early microbial life.”
Barite rock from the Dresser band. (Helge Mißbach)
While scientists have long hypothesized how organic molecules could act as substrates for primary microbes and their metabolic processes, direct evidence has so far proved very elusive.
To investigate, Mißbach and research colleagues examined inclusions in the barites of the Dresser Formation, with the chemically stable mineral capable of storing fluids and gases inside the rock for billions of years.
Using a range of techniques to analyze barium samples – including gas chromatography-mass spectrometry, microthermometry and stable isotope analysis, the researchers discovered what they describe as an “intriguing diversity of organic molecules with known or inferred metabolic relevance”.
These included the organic compounds acetic acid and methanethiol, in addition to numerous gases, including hydrogen sulfide, which may have had biotic or abiotic origins.
(Mißbach et al., Nature Communications, 2021)
Above: Baritei rock, indicating a close association with stromatolites.
Although it may be impossible to be sure of precise connections, the proximity of these inclusions in barytic rock and adjacent organic accretions called stromatolites suggest that ancient chemicals, once transported inside hydrothermal fluids, may have influenced primitive microbial communities.
“Indeed, many of the compounds found in barite-hosted fluid inclusions … would have provided ideal substrates for sulfur-based microbes and methanogens previously proposed as players in the dresser environment,” the researchers write in their study.
In addition to chemicals that could have acted as nutrients or substrates, other compounds found in the inclusions could have served as “basic elements” for various carbon-based chemical reactions – processes that could have triggered microbial metabolism, producing energy sources, such as lipids, that could be broken down by life forms.
“In other words, the essential ingredients of methyl thioacetate, a proposed critical agent in the emergence of life, were available in Dresser environments,” the team explains.
“It could have transmitted the basics for chemoautotrophic carbon fixation and therefore anabolic carbon sequestration in biomass.”
The findings are reported in Communications about nature.