On an outcrop of exposed volcanic and sedimentary rock on the eastern shores of Hudson Bay in northern Quebec, researchers have discovered what may be the earliest fossilized lifeforms ever discovered. These microbial ancestors lived between 3.75 and 4.28 billion years ago, only 300 million years after the Earth itself formed – a blink of an eye in geologic timescales. If life developed this rapidly on Earth, it suggests that abiogenesis – the process by which non-living matter becomes a living organism – is potentially ‘easy’ to achieve, and life in the Universe may be more common than we thought.
The evidence for these early lifeforms comes from the Nuvvuagittuq Supracrustal Belt, a rocky outcrop that was once deep under the ocean close to a system of hydrothermal vents. The Belt has since risen to the surface, after many millennia of geologic change and tectonic activity. In 2017, researchers discovered tiny filaments in the Belt which appeared to have been made by bacteria, but the evidence was inconclusive. They could not rule out chemical processes that might create similar patterns in the rock.
Since then, the team has been examining samples from the Belt more carefully, and this month released a new paper in Science Advances strengthening the case for life. Not only did they find more examples of the filaments, spheres, and tubes like those initially described in 2017, but they also found a larger, more complex structure, ‘tree-like’ in shape with parallel branches, that is unlikely to have a chemical explanation.
This ‘tree-like’ structure is among the oldest microfossils on Earth. The microbes that created it lived on the sea-floor near hydrothermal vents, and they metabolised iron, sulfur and carbon dioxide. Nuvvuagittuq Supracrustal Belt, Québec, Canada. Credit: D. Papineau.
Not only does the new research suggest a biological origin for the fossils, it also suggests early diversity, with lifeforms obtaining energy from different sources. Mineralized chemical by-products in the rock suggest that microbes in the Belt lived off iron, sulfur, and maybe carbon dioxide and light – a form of photosynthesis.
Lead author Dr. Dominic Papineau (UCL) explains that “using many different lines of evidence, our study strongly suggests a number of different types of bacteria existed on Earth between 3.75 and 4.28 billion years ago.”
To rule out geological and chemical explanations for the fossils, the team put the samples through various tests. Viewing paper-thin slices of the rock under microscopes, they determined that the filaments are better preserved in fine quartz, which is less susceptible to metamorphic change than rough quartz. This suggests that the filaments were not created through metamorphism (the heating and squeezing of rock). Similarly, they looked at the levels of rare earth elements in the Belt and compared them to similarly-aged rock formations elsewhere in the world, to more accurately date the site and confirm that the fossils were indeed as old as they appear.
After completing this careful program of analysis, the team believes that living organisms are the most likely explanation for the filaments in the Belt, but there always is room for uncertainty. The possibility remains that the ‘fossils’ were formed through non-living processes.
The researchers are confident that even if they are abiotic, they still “could indicate complex prebiotic forms on early Earth.”
Haematitic chert (an iron-rich and silica-rich rock), which contains tubular and filamentous microfossils. The dark green volcanic rock in the top right was formed by hydrothermal vents on the seafloor. Nuvvuagittuq Supracrustal Belt, Québec, Canada. Canadian quarter for scale. Credit: D. Papineau.
The discovery has potentially substantial implications for the search for life elsewhere in the Solar System. It means that in the right conditions, life can form very fast, and could be anywhere. But you don’t have to take my word for it. The paper itself concludes that if “only a few hundred million years are needed for life to evolve to an organized level on a primordial habitable planet…such microbial ecosystems could exist on other planetary surfaces where liquid water interacted with volcanic rocks, and…extraterrestrial life may be more widespread than previously thought.”
You can read the full study here:
https://www.science.org/doi/10.1126/sciadv.abm2296
Press Release:
https://www.ucl.ac.uk/news/2022/apr/diverse-life-forms-may-have-evolved-earlier-previously-thought