Claims published on Thursday in Nature that the world's oldest fossils have been discovered have been challenged by leading experts in the field.
Scientists at University College London claim to have found the remnants of structures made by micro-organisms that are the oldest fossils on Earth. At between 3.8 and 4.3 billion years old, the finding is bound to stir primordial questions about the origin of life on Earth.
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Scientists find world's oldest fossils
A team of scientists at University College London claim to have found the remnants of structures made by micro-organisms that could be the oldest fossils on Earth. Vision courtesy Nature.
"Our discovery supports the idea that life emerged from hot, sea-floor vents shortly after planet Earth formed," said doctoral student Matthew Dodd, the lead author of the study published on Thursday in Nature.
However, Professor Malcolm Walter, the founding director of the Australian Centre for Astrobiology, has expressed doubts about the findings, saying that in his view: "It's not believable."
![The rock structure in Canada where the fossils were found.](/web/20170311051028im_/http://www.theage.com.au/content/dam/images/g/u/n/w/a/o/image.related.articleLeadwide.620x349.gunu0j.png/1488391654526.jpg)
He said: "Every statement in the paper is hedged. No normally sceptical scientist can accept the evidence as presented."
The "putative microfossils" (as they are described in the paper) were found in quartz layers within a belt of rock in Quebec, Canada. The Nuvvuagittuq suprastructural belt is thought to be one of the oldest rock formations on the planet.
The authors say the fossils are not remnants of the single-celled organisms, but rather the tubes and filaments they formed as they fed on hydrogen sulfide and iron around hot vents on the ocean floors.
"This is probably similar to where life on Earth began," said Professor Franco Pirajno, a co-author of the study from the University of Western Australia.
![Filaments from the Canadian rocks that scientists say show structural evidence of early bacterial life.](/web/20170311051028im_/http://www.theage.com.au/content/dam/images/g/u/n/w/a/w/image.related.articleLeadwide.620x349.gunu0j.png/1488391654526.jpg)
"The date of these findings is mind-boggling," he said.
However, Professor Walter's criticisms of the paper are supported by Professor Martin Van Kranendonk head of the school of biological, earth and environmental studies at the University of NSW.
![Professor Franco Pirajno, geologist at the University of Western Australia, in the Earaheedy Basin in Western Australia.](/web/20170311051028im_/http://www.theage.com.au/content/dam/images/g/u/o/1/r/g/image.related.articleLeadwide.620x349.gunu0j.png/1488391654526.jpg)
Professor Van Kranendonk is a recognised global expert on microfossils.
"They haven't proved these structures are of biological origin," he said. "The rocks in which they have been found are strongly recrystalised."
![Some of the rocks from Quebec.](/web/20170311051028im_/http://www.theage.com.au/content/dam/images/g/u/n/w/a/q/image.related.articleLeadwide.620x349.gunu0j.png/1488391654526.jpg)
Professor Walter said these rocks are extremely altered and have been cooked deep in the crust at more than 500 degrees. This, he said, destroys their original structures.
"In these sorts of studies you usually start with the most well-preserved rocks. These rocks are unusually badly preserved," he said.
![Emeritus Professor Malcolm Walter from UNSW.](/web/20170311051028im_/http://www.theage.com.au/content/dam/images/g/u/o/1/u/4/image.related.articleLeadwide.620x349.gunu0j.png/1488391654526.jpg)
Professor Pirajno said: "I'm not surprised at the criticisms. I did expect something like that. But you have to put the whole picture together.
"No.1, [the research shows] the structures were formed in a submarine environment; two, there are thermal springs; and three, we have these tubular features. What else could they be?
![The area of Canada in northern Quebec where the structures were discovered.](/web/20170311051028im_/http://www.theage.com.au/content/dam/images/g/u/n/w/a/m/image.related.articleLeadwide.620x349.gunu0j.png/1488391654526.jpg)
"Of course you could dispute it, but this looks like a pretty good interpretation."
Professor Pirajno's role in the study was to assist Mr Dodd and co-author Dominic Papineau from University College London to compare the findings in Canada to established fossilised stromatolite structures in the Pilbara and Earaheedy basin in Western Australia.
"They are exactly the same structure as the 1.8 billion-year-old Earaheedy structures and the 3.5 billion-year-old Pilbara structures," Professor Pirajno said.
Given how old the Canadian fossils are, there is bound to be debate, he said. "This is what science is all about. It's not a religion, we debate these things," he said.
Dr Papineau from UCL said: "We found filaments and tubes inside centimetre-sized structures, all of which we think are the products of putrefaction [by bacteria]. They are mineralogically identical to those in younger rocks from Norway, the Great Lakes and Western Australia."
However, Professor Van Kranendonk said that while gross similarities can survive the changes these rocks have undergone, the type of recrystalisation they have experienced would change their mineralogy.
"I'm just not convinced at all that it's only biology that can make these structures," said Professor Van Kranendonk, who is the director of the Australian Centre for Astrobiology.
Professor Pirajno said: "Martin is entitled to his opinion. But the work the guys in London have done is good. It's not 100 per cent but it's good enough to have it published. It's gone through a lot of reviews."
Whatever the truth that lies behind these rocks, it is bound to prompt further discussion in scientific circles about how – and when – life started on Earth.
Associate Professor Rowena Ball from Australian National University said the date of the findings would imply cellular life developed rather quickly.
"These are very interesting findings, indeed. They imply that the steps from the molecular evolution to the RNA world, lipids, and peptides to membrane-bound cellular life with DNA may have happened within only a few million years," said Associate Professor Ball, who holds a joint position in the schools of mathematics and chemistry at the ANU.
"My team is currently doing research that supports this view," she said.
The strength of the public criticism voiced by professors Van Kranendonk and Walter is unusual for a paper published in Nature.