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Paleontologists have discovered the exceptionally well-preserved filamentous microfossils, 3.42 billion years old, in a system of paleosubmarine hydrothermal veins in what is now South Africa; the filaments colonized the walls of the conduits created by the hydrothermal fluid at low temperature; combined with their morphological and chemical characteristics, they can be considered as the oldest microorganisms cycling methane, most likely methanogens.
The 3.42 billion-year-old filamentous microfossils of the Barberton greenstone belt in South Africa. Image credit: Cavalazzi et al., doi: 10.1126 / sciadv.abf3963.
“We have found exceptionally well-preserved evidence of fossilized microbes that appear to have thrived along the walls of cavities created by hot water from hydrothermal systems a few meters below the seabed,” said Professor Barbara Cavalazzi, researcher at Dipartimento di Scienze Biologiche, Geologiche e Ambientali at the Università di Bologna and at the Department of Geology at the University of Johannesburg.
“Subterranean habitats, heated by volcanic activity, likely hosted some of Earth’s earliest microbial ecosystems and this is the oldest example we have found to date.”
Professor Cavalazzi and his colleagues have discovered 3.42 billion-year-old (Paleoarchean) filamentous microfossils in two thin layers in a rock collected in the Barberton greenstone belt in South Africa.
All the filaments are embedded in chert (α-quartz) and are composed of moderately ordered carbon, consistent with ancient permineralized cellular remains.
They have an outer sheath and a distinct nucleus, compatible with a cell wall or membrane around intracellular or cytoplasmic material.
The chemical composition of the filaments includes most of the major bioessential elements.
The presence of organic nickel compounds is consistent with primordial metabolisms. The absence of phosphorus could be the result of the trapping or leaching of this bioessential element.
“The interaction of cooler seawater with warmer subterranean hydrothermal fluids would have created a rich chemical soup, with varying conditions leading to multiple potential microhabitats,” the researchers said.
“The filament clusters were found at the end of sharp hollows in the walls of the cavity, while the individual filaments were distributed on the floor of the cavity.”
“The concentrations of nickel in organic compounds provide further evidence of primordial metabolisms and are consistent with the nickel content found in modern microbes, called Archaea, which live in the absence of oxygen and use methane for their metabolism. “
“Although we know that Archaea prokaryotes can be fossilized, we have extremely limited direct examples,” added Professor Cavalazzi.
“Our findings may expand the record of Archaea fossils for the first time around the time life first appeared on Earth.”
“As we also find similar environments on Mars, the study also has implications for astrobiology and the chances of finding life beyond Earth.”
Results appear in the journal Scientists progress.
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Barbara cavalazzi et al. 2021. Cellular remains in an underwater hydrothermal environment about 3.42 billion years old. Scientists progress 7 (29): eabf3963; doi: 10.1126 / sciadv.abf3963
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