Tiny tubes and filaments in some Canadian rock appear to be the oldest known fossils, giving new support to some ideas about how life began, a new study says.
The features are mineralized remains of what appear to be bacteria that lived some 3.77 billion to 4.28 billion years ago, the scientists 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.
Such early-life findings are not as clear-cut as, say, digging up a dinosaur bone. The key question is always whether the rock features were really produced by living things. The new study hasn't convinced everybody.
The new results come from examining rock found along the eastern shore of Hudson Bay in northern Quebec. The microscopic filaments and tubes, composed of an iron oxide called hematite, appeared within a rock type called jasper. A single strand may represent a chain of cells.
Matthew Dodd of University College London, an author of the study published Wednesday by Nature, said the microbes lived near a vent in the seafloor where water was heated by a volcano. Since the fossil are nearly 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.
He and colleagues presented several lines of evidence to support the idea that the filaments and tubes are signatures of past life. But two experts who've previously reported similar findings said they're not convinced.
"I would say they are not fossils," Martin J. Van Kranendonk of the University of New South Wales in Australia, who reported the Greenland findings last year, wrote in an email.
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The paper's evidence for a biological origin falls short, he said.
Abigail Allwood, a NASA geologist, said the authors have produced "one of the most detailed cases yet made" for evidence of life in rocks older than 3.5 billion years.
But "it's an extraordinary claim to make and you do need extraordinary evidence," she said.
While the rock features could be signs of past life, she said, "I think the jury is still out a little bit."
Stronger evidence for ancient fossils comes from several findings in rocks at around 3.5 billion years old, she said.
