Scientists believe they have found evidence of microbes thriving near hydrothermal vents on Earth’s surface just 300 million years after the planet was formed – the strongest evidence so far that life began much earlier than previously thought.
If confirmed, this would imply that the conditions necessary for the emergence of life are relatively basic.
“If life appears relatively quickly, under the right conditions, it increases the chances of life existing on other planets,” said Dominique Papino of University College London, who is leading the study.
Five years ago, Papino and his colleagues announced that they had found microfossils in iron-rich sedimentary rocks from the supracrustal belt Nuvvuagittuq in Quebec, Canada. The team speculates that these small threads, buttons and tubes of iron oxide, called hematite, may have been made by bacteria living around hydrothermal vents that used iron-based chemical reactions to produce their energy.
Scientific dating of the rocks suggests that they are at least 3.75 billion years old and probably 4.28 billion years old, the age of the volcanic rocks in which they are embedded. Previously, the oldest reported microfossils date to 3.46 billion and 3.7 billion years ago, potentially making Canadian specimens the oldest direct evidence of life on Earth.
Further analysis of the rock now revealed a much larger and more complex structure – a stem with parallel branches on one side that is almost a centimeter long – as well as hundreds of curved spheres or ellipsoids parallel to the tubes and threads.
“One thing I think is amazing is the large size of the tectonic branched structure, which is a few millimeters, if not more than a centimeter,” said Papino, adding that they have some resemblance to threads made from Mariprofundus ferrooxydans, a modern bacterium. , found in iron-rich deep marine environments, in particular hydrothermal vents. “But ours are much bigger, much thicker,” he said.
“I think what we’re seeing is a microbial community – that they’ve worked together, and because the fibers grow from groups of these cells, they mix and make a bigger, thicker hematite thread.
The team also identified mineralized chemical by-products in the rock, according to these ancient microbes, living on iron, sulfur and possibly also carbon dioxide and light through a form of oxygen-free photosynthesis.
Taken together, these new discoveries could suggest that a variety of microbial life may have existed only 300 million years after the formation of the Earth.
“I believe it makes sense that they are as old as the volcanic rocks that make them up, which would be 4.28 billion years,” Papino said. “Pushing the clock back is very important because it tells us that it takes a very short time for life to appear on a planetary surface. Very soon after [Earth formed] in these hydrothermal vents there was a microbial life that ate iron and sulfur.
However, not everyone is convinced that the structures are of biological origin. Although somewhat similar to other ancient and modern examples of bacteria, “these comparisons are in rocks or environments that have not undergone a very high degree of metamorphism. [a process involving extreme temperature and pressure] from the Nuvvuagittuq rock, ”said Prof. Francis Westal, an expert on ancient fossil bacteria at the French National Center for Research.
She said: “I am particularly concerned about the parallelism of the fibers – they seem to follow the crystal lattice of the host mineral. This is not a microbial characteristic, so fibers can be a metamorphic artifact.
On the other hand, the sulfur identified by the team may be of biological origin. Westall said: “If their sulfur isotope data are correct, then the chemical sediments presented by Nuvvuagittuq jasper may have contained traces of life associated with hydrothermal vents.