The World's Oldest Fossils Unearthed in Canada

Hematite tubes from the NSB hydrothermal vent deposits that represent the oldest microfossils and evidence for life on Earth. Image credit Matthew Dodd University College London

The tiny fossils - half the width of a human hair and up to half-a-millimetre in length - take the form of blood-red tubes and filaments formed by ocean-dwelling bacteria that fed on iron. Since the fossil are almost as old as Earth, which formed some 4.5 billion years ago, the finding supports previous indications that life may have begun in such an environment, he said. That would surpass the 3.7 billion years assigned to some other rock features found in Greenland, which were proposed to be fossils last August.

What is claimed to be the oldest evidence of life on Earth yet found backs the idea that the first microbes originated around hydrothermal vents on the seafloor - but the work is already proving controversial.

However, some experts were not convinced that the filaments and tubes were really fossils, rather than just the consequences of geological processes.

Of course, it's best not to get too carried away in daydreams until we're more certain about what the researchers have found in these Canadian rocks.

The fossilized remains were found near what's thought to have once been a hydrothermal vent, where swirling heat, chemicals and minerals may have given rise to the first single-celled organisms. Like modern iron-dependent bacteria, they "would have literally "eaten" the iron ... in the same sense that we eat cake", Papineau says, adding the bacteria could have formed rust-colored mats like those seen today. Intriguingly, the sort of life that Dr Papineau and his colleagues think they have found is very different from the sort that built the stromatolites. Scientists found the ancient fossils in a rock in the Nuvvuagittuq Supracrustal Belt, a remote region of Quebec, Canada.

Other clues that the tubes and filaments were made by biological processes included the presence of granules inside the rocks that contain carbonaceous material.

"All these independent lines of evidence tell us that these microfossils are indeed biological in origin", Dodd says.

University College London researchers who discovered the fossil say life on Earth likely started up to 4.5 billion years ago while Mars still had oceans and an atmosphere. However, some scientists are casting doubt on what the findings truly mean.

Two primary pieces of evidence suggest that ancient bacteria are responsible for the NSB samples. That makes these the oldest known fossils and possibly the oldest known evidence for life on Earth. Hydrothermal vents deep beneath the oceans have always been thought to be where life originated, leading Matthew Dodd and colleagues to search where they did. One of the biggest questions in science is whether life is an inevitable and common effect of the laws of chemistry, or a lucky one-off confined to Earth alone. "Given this new evidence. ancient submarine-hydrothermal vent systems should be viewed as potential sites for the origins of life on Earth, and thus primary targets in the search for extraterrestrial life". The filaments and tubes are much simpler than the microbial structures seen around modern hydrothermal vents. Preserved within this belt are iron formations formed in settings analogous to hydrothermal vents today. "It gives me ... high hopes of finding life elsewhere in the universe".

Previously the oldest reported microfossils, from Western Australia, were dated at 3,460 million years old.

"It's indeed possible that life started on Mars as well as the Earth, but then fizzled out - maybe leaving some traces that we will discover from future probes", he said. If both papers are confirmed, Slack explained, that means life not only existed early in Earth's history, but was diverse enough to include both chemosynthetic and photosynthetic bacteria. Between 4 and 3.8 billion years ago, the planet was subjected to what's called the "Late Heavy Bombardment", a time when asteroids and comets flew through the solar system and barraged every body they struck.

Any claim for the earliest life on Earth attracts scepticism.

What's more intriguing, however, is how the finding bolsters the case for searching for life on Mars, and may even narrow down the kinds of places on the red planet where we should look.



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