Paleontologists may have just uncovered the trace fossils of the oldest creatures on Earth: 4.28 billion years old.

The oldest life

Field of microscopic filamentous microfossils inside a rounded concretion from the jasper rock in the Nuvvuagittuq Supracrustal Belt in Québec, Canada. The filaments are composed of hematite (red lines), and are located in a quartz layer (white) surrounded by magnetite (black), where both hematite and magnetite are iron oxide minerals. Image credits: Matthew Dodd.

It was a time when the Moon was still freshly formed, and liquid water likely flowed on Mars. The Earth was, at best, an unfriendly and bizarre place. Yet somewhere beneath the surface, in the proximity of a hydrothermal vent close to what is today Canada, these bacteria found a way to thrive.

The fossils were discovered in the Nuvvuagittuq Supracrustal Belt (NSB) on the coast of Hudson Bay in the northern parts of Canada’s Quebec province. The supracrustal belt contains some of the world’s oldest sedimentary rocks, deposits of sand and gravel which accumulated in the earliest stages of Earth’s geological history — more than 4 billion years ago. These structures were slowly uplifted through geological processes, ultimately emerging from the sea.

“The fact we unearthed them from one of the oldest known rock formations suggests we’ve found direct evidence of one of Earth’s oldest life forms,” says University College London (UCL) Earth scientist Dominic Papineau, lead researcher on a study published today in Nature Paleontology, in a press release.

“This discovery helps us piece together the history of our planet and the remarkable life on it, and will help to identify traces of life elsewhere in the universe.”

Ancient life: These clumps of iron and filaments show similarities to modern microbes. Image credits: Matthew Dodd.

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Indeed, the idea that life on Earth emerged around hydrothermal vents (or… one hydrothermal vent?) is one of the oldest theories regarding the spawning of life on our planet, competing with panspermia — the theory that life was brought by an asteroid or some other celestial body. If this finding is confirmed, it certainly supporting the former.

“Our discovery supports the idea that life emerged from hot, seafloor vents shortly after planet Earth formed,” says Matthew Dodd, first author on the study and a UCL Ph.D. student. “This speedy appearance of life on Earth fits with other evidence of recently discovered [3.7-billion]-year-old sedimentary mounds that were shaped by microorganisms.”

Evidence and skepticism

Basically, the team took samples of rock from these deposits and cut thin slices, which they then analyzed, finding two key pieces of evidence which indicate the presence of bacteria fossils. The first is the presence of calcium and carbon minerals, such as graphite, apatite, and carbonate — minerals which are widely associated with fossils. Of course, these minerals often show up without any connection to fossils, which is why the second piece of evidence is even more convincing: they found the fossils within small spheroidal structures in the rock. This is a trademark of bacteria, and similar traces were found in other places of the world. The structure also bare similarities to modern bacteria living around vents.

“We found the filaments and tubes inside centimeter-sized structures called concretions or nodules, as well as other tiny spheroidal structures, called rosettes and granules, all of which we think are the products of putrefaction,” says Papineau. “They are mineralogically identical to those in younger rocks from Norway, the Great Lakes area of North America and Western Australia.”

The study brings another interesting conclusion: these bacteria lived when liquid water flowed on Mars… so isn’t there a good chance that similar creatures emerged on the Red Planet? We don’t have an answer, and we don’t know whether a similar process occurred on Mars or if Earth is some kind of exception.
“These discoveries demonstrate life developed on Earth at a time when Mars and Earth had liquid water at their surfaces, posing exciting questions for extraterrestrial life,” says Dodd. “Therefore, we expect to find evidence for past life on Mars 4,000 million years ago, or if not, Earth may have been a special exception.”

Still, not everyone is convinced. There’s always an element of skepticism floating in the air when it comes to this type of study. For starters, it’s surprising to find fossils in hematite, an iron oxide, when there wasn’t that much oxygen to go around. The previous oldest found fossil was 3.7 billion years old, which is a huge difference.

Prof Nicola McLoughlin from Rhodes University, South Africa, commented on what she sees as shortcomings of this study:

“The morphology of these argued iron-oxidising filaments from Northern Canada is not convincing,” she told BBC News. In recent deposits we see spectacular twisted stalks, often arranged in layers, but in the highly metamorphosed rocks of the Nuvvuagittuq belt the filaments are much simpler in shape. The associated textural and geochemical evidence of graphite in carbonate rosettes and magnetite-haematite granules is careful work, but provides only suggestive evidence for microbial activity; it does not strengthen the case for the biogenicity of the filaments.”

She also mentioned that the age of the rocks in which the alleged fossils were found is also controversial, and they might not be as old as Papineau claims.

Thing is, it’s always gonna be difficult to prove this kind of thing beyond the shadow of a doubt. It’s extremely challenging to show that 4 billion-year-old micrometre-scale haematite tubes and filaments are or aren’t fossils. But overall, the evidence is convincing. Not beyond contention, but certainly putting up a good fight. The study was published in Nature, which means it was peer-reviewed.

Journal Reference: Matthew S. Dodd, Dominic Papineau, Tor Grenne, John F. Slack, Martin Rittner, Franco Pirajno, Jonathan O’Neil & Crispin T. S. Little — Evidence for early life in Earth’s oldest hydrothermal vent precipitates. doi:10.1038/nature21377