The heat and minerals expelled by hydrothermal vents allow creatures to survive without sunlight at the ocean's floor. Ralph White/ Corbis Documentary/ Getty Images
Researchers have combed the planet’s surface in search of the beginnings of life on Earth. But some microfossils discovered in hydrothermal veins in South Africa suggest that some of the earliest organisms lived underground instead. The finding could also offer hints of where to look for signs of life on other planets.
The Onverwacht Group in South Africa’s Barberton Greenstone Belt is a well-known repository for cellular remnants tracing back more than three billion years. Located in north-eastern South Africa, it is home to some of the oldest rocks on Earth, which were submerged and part of the seafloor at the time. As a paleontologist interested in ‘extremophile’ species that favour inhospitable environments, Barbara Cavalazzi of the University of Bologna jumped at the chance to investigate, along with a collaborator, Axel Hofmann, of the University of Johannesburg.
Cavalazzi’s initial inspection of samples from 3.42-billion-year-old quartz deposits from below the ancient seafloor revealed fine, filamentous structures resembling debris from fossilized microorganisms. Back at the lab, the researchers subjected these to much more intensive analysis with microscopy and spectroscopy. Their analyses of the structure and chemical composition of these filaments, and in particular the traces of carbon, hydrogen and oxygen, strongly supported the theory that they are remnants from ancient microbes with a methane-based metabolism.
Although not decisive proof of life, the traces uncovered here are highly similar to other ancient remnants of methane-consuming bacteria, and Cavalazzi believes that other similar microbial ‘fingerprints’ remain to be found. “We had the chance to show that the subsurface environments billions of years ago could have been a suitable niche for life,” she says, adding that these represent a new frontier in the search for ancient organisms. “It is even possible that traces of primitive life are preserved in similar settings on Mars,” adds Cavalazzi.
