Researchers have discovered organic molecules trapped in incredible ancient rock formations in Australia, revealing what they say is the first detailed evidence of early chemical constituents that could support the earth’s original microbial life forms.
The discovery, made in the 3.5 billion-year-old Dresser formation of Pilbara Craton in Western Australia, contributes to a significant amount of research that points to the ancient life in this part of the world – which is one of only two pristine, exposed deposits of land on earth date from the Archean Eon.
In recent years, the hydrothermal rock of the Dresser Formation has shown repeated signals of what appears to be the earliest 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 cause such primordial organisms to exist, by finding biologically relevant organic molecules in barite deposits, a mineral formed by various processes, including hydrothermal phenomena.
“In the field, the barite is directly associated with fossilized microbial mats, and it smells like rotten eggs when freshly scraped,” explains geobiologist Helge Mißbach of the University of Cologne in Germany.
“We therefore suspected that it contained organic matter that would potentially serve as nutrients for early microbial life.”
Barite rock from the Dresser Formation. (Helge Mißbach)
While scientists have long hypothesized how organic molecules can act as substrates for primordial microbes and their metabolic processes, direct evidence so far has been largely elusive.
To investigate this, Mißbach and fellow researchers investigated the inclusion of barites from the Dresser Formation, with the chemically stable mineral that can store liquids and gases in the rock for billions of years.
Using a range of techniques to analyze the barite samples – including gas chromatography-mass spectrometry, microthermometry and stable isotope analysis, the researchers found what they described as an “interesting diversity of organic molecules with a known or derived metabolic relevance”.
These include the organic compounds acetic acid and methanethiol, in addition to numerous gases, including hydrogen sulfide, which could have biotic or abiotic origin.
(Mißbach et al., Nature Communications, 2021)
Above: the Barite rock, indicating close association with stromatolites.
Although it may be impossible to be sure of the exact links, the proximity of these inclusions in the barite rock and adjacent organic growth, called stromatolites, indicates that the ancient chemicals, first carried in hydrothermal fluids, may have -microbial communities.
“Indeed, many compounds discovered in the barite-hosted fluid inclusions … would provide the ideal substrates for the sulfur-based and methanogenic microbes previously proposed as players in the Dresser environment,” the researchers write in their study.
In addition to chemicals that may have acted as nutrients or substrates, other compounds found in the inclusions may also be ‘building blocks’ for various chemical reactions to carbon – processes that could initiate microbial metabolism, by producing energy sources, such as lipids, which by life forms can be broken down.
“In other words, essential ingredients of methylthioacetate, a proposed critical agent in the origin of life, were available in the Dresser environments,” the team explains.
“They may have transferred the building blocks for chemo-autotrophic carbon sequestration and thus anabolic uptake of carbon into biomass.”
The findings are presented in Nature communication.