Microbes related to the methane cycle already lived in a hydrothermal system under the seabed 3.420 million years ago, a discovery that expands the boundaries of potentially habitable environments, not only in the Land primitive, but on other planets like Mars.
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A team led by the University of Bologna (Italy) has discovered fossil remains that are the oldest evidence of this type of microorganism, according to a study published today Scientific advances.
The remains were found in the greenstone belt of Barberton (South Africa), an area near the border with Swaziland and Mozambique, which preserves some of the oldest and best preserved sedimentary rocks on the planet.
The team found “exceptionally well-preserved” evidence of these fossilized microbes in the cavities created by hot water from hydrothermal systems just a few meters below the seafloor, noted lead study author Barbara Cavalazzi.
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Subterranean habitats, heated by volcanic activity, are likely home to some of Earth’s earliest microbial ecosystems and “this is the oldest example” they have found to date, he said.
The interaction of cooler seawater with warmer subsurface hydrothermal fluids would have created a “rich chemical soup”, with variations in conditions giving rise to multiple potential microhabitats.
Chemical analysis shows that the filaments found on the walls and floor of the cavity contain “most of the major elements necessary for life.” Nickel concentrations in organic compounds provide further proof of primordial metabolisms and are consistent with the nickel content found in modern microbes, known as prokaryotes Archaea, that live in the absence of oxygen and use methane for their metabolism.
“Although we know that Archaea prokaryotes can fossilize, we have very few direct examples,” said Cavalazzi, for whom these discoveries could extend the Archaea fossil record for the first time to the time when life emerged on Earth.
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The expert stressed that, as there are also “similar environments on Mars, the study has implications for astrobiology and the possibilities of finding life beyond Earth.”
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