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takyon writes:

Geologists Question 'Evidence Of Ancient Life' In 3.7 Billion-Year-Old Rocks

The oldest evidence of life on Earth probably isn't found in some 3.7 billion-year-old rocks found in Greenland, despite what a group of scientists claimed [DOI: 10.1038/nature19355] [DX] a couple of years ago. That's according to a new analysis [DOI: 10.1038/s41586-018-0610-4] [DX], published Wednesday in the journal Nature by a different team of experts. This second group examined structures within the rock that were thought in 2016 to have been produced by communities of single-celled microbes that grew up from the bottom of a shallow, salty sea. A three-dimensional look at these structures shows that instead of having a telltale upside-down ice-cream cone shape — the kind produced by microorganisms — they are shaped like a Toblerone candy bar.

"They're stretched-out ridges that extend deeply into the rock," said Joel Hurowitz, a geochemist at Stony Brook University in New York and an author of Wednesday's paper. "That shape is hard to explain as a biological structure and much easier to explain as something that resulted from rocks being squeezed and deformed under tectonic pressures." Asked what the chances were that the structures were created by ancient microbes, astrobiologist Abigail Allwood — of NASA's Jet Propulsion Laboratory and lead author of this second analysis — said: "I don't think there's much chance at all."

[...] All of this is vigorously disputed by the researchers who originally claimed that the Greenland rocks contained the world's oldest fossils. They stand by that claim and say that Allwood and her colleagues based their work on just a cursory, one-day visit to the site. [...] Vickie Bennett, of the Australian National University, added that she found the new study "disappointing" and "unfortunate" in that it "only serves to confuse" the earlier research that she and her colleagues did on these ancient rocks. "Basically they did not look at the same rocks — and the details matter," Bennett told NPR in an email. In her view, the rocks in the current study are a "poor-cousin equivalent to the rocks of our original study" and the new analysis "was not conducted with care."

The article does not address evidence found in Quebec in 2017, dated to between 3.77 and 4.28 billion years ago.

Also at USA Today.

Previously: 3.7 Billion-Year-Old Fossil Found
Earliest Known Evidence for Microbial Life on Land: 3.48 Billion Years Old
Analysis of Microfossils Finds that Microbial Life Existed at Least 3.5 Billion Years Ago - "However, the complexity of the fossilized microbes suggests that life arose much earlier, possibly as far back as 4 billion years ago."

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