3.42-Billion-Year-Old Filamentous Microfossils Found in South Africa
Paleontologists have discovered the exceptionally well-preserved, 3.42-billion-year-old filamentous microfossils in a paleo-subseafloor hydrothermal vein system in what is now South Africa; the filaments colonized the walls of conduits created by low-temperature hydrothermal fluid; combined with their morphological and chemical characteristics, they can be considered the oldest methane-cycling microorganisms, most likely methanogens.
“We found exceptionally well-preserved evidence of fossilized microbes that appear to have flourished along the walls of cavities created by warm water from hydrothermal systems a few meters below the seafloor,” said Professor Barbara Cavalazzi, a researcher in the Dipartimento di Scienze Biologiche, Geologiche e Ambientali at the Università di Bologna and the Department of Geology at the University of Johannesburg.
“Sub-surface habitats, heated by volcanic activity, are likely to have hosted some of Earth’s earliest microbial ecosystems and this is the oldest example that we have found to date.”
Professor Cavalazzi and colleagues found 3.42-billion-year-old (Paleoarchean Era) filamentous microfossils in two thin layers within a rock collected from the Barberton Greenstone Belt in South Africa.
All of 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 core, consistent with a cell wall or membrane around intracellular or cytoplasmic matter.
The chemical composition of the filaments includes most of the major bioessential elements.
The presence of nickel-organic compounds is consistent with primordial metabolisms. The absence of phosphorus could be the result of scavenging or leaching of this bioessential element.
“The interaction of cooler sea-water with warmer subsurface hydrothermal fluids would have created a rich chemical soup, with variations in conditions leading to multiple potential micro-habitats,” the researchers said.
“The clusters of filaments were found at the tips of pointed hollows in the walls of the cavity, whereas the individual filaments were spread across the cavity floor.”
“The concentrations of nickel in organic compounds provide further evidence of primordial metabolisms and are consistent with nickel-content found in modern microbes, known as Archaea, that 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,” Professor Cavalazzi added.
“Our findings could extend the record of Archaea fossils for the first time into the era when life first emerged 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.”
The findings appear in the journal Science Advances.
Barbara Cavalazzi et al. 2021. Cellular remains in a ~3.42-billion-year-old subseafloor hydrothermal environment. Science Advances 7 (29): eabf3963; doi: 10.1126/sciadv.abf3963