Oldest ever methane-cycling microfossils discovered

A blue background with black splodges
Optical microscope image of the filamentous microfossils. Credit: B. Cavalazzi
A landscape with small hills
Image of the locality of the study area in the Barberton Greenstone Belt in South Africa. Credit: A. Hofmann

Researchers have discovered the fossilised remains of 3.4-billion-year-old methane-cycling microbes that lived in a hydrothermal system beneath the ancient seafloor – the oldest microfossils of this type found to date.

According to the study, published in Science Advances, these microfossils provide evidence that this type of life can survive in extreme volcanic environments – maybe even Mars.

“We found exceptionally well-preserved evidence of fossilised microbes that appear to have flourished along the walls of cavities created by warm water from hydrothermal systems a few metres below the seafloor,” says Barbara Cavalazzi of the University of Bologna, Italy, and the University of Johannesburg, South Africa, who led the study.

“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.”

Read more: Living fossil discovered below Earth’s surface

A rck with a hammer next toit. The rock is light and dark grey
Image of the outcrop from which the rock sample was taken in the Barberton Greenstone Belt in South Africa. Credit: Cavalazzi et al.

The researchers analysed microfossils from two thin layers within a rock collected from the Barberton Greenstone Belt in South Africa’s east.

The microfossils had a carbon-rich outer sheath with a distinct core, much like a cell membrane or wall, and chemical analysis showed that they contained most of the major elements needed for life. There was evidence of a primordial metabolism that was somewhat like modern microbes called Archaea prokaryotes, which live without oxygen and “breathe” methane instead.

“Although we know that Archaea prokaryotes can be fossilised, we have extremely limited direct examples. Our findings could extend the record of Archaea fossils for the first time into the era when life first emerged on Earth,” says Cavalazzi.

“As we also find similar environments on Mars, the study also has implications for astrobiology and the chances of finding life beyond Earth.”

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