Oldest fossils or just rocks? Scientists at odds over Greenland site
It was an extraordinary claim: Scientists studying a rock formation in Greenland said they had discovered the Earth’s oldest fossils, a series of small, coneshaped structures left by microbial mats some 3.7 billion years ago.
The announcement in 2016 in the pages of the journal Nature generated global media coverage and potentially carried cosmic significance. These alleged fossils suggested life appeared on Earth soon after the planet cooled enough to be habitable. The implication was that, given the right conditions, life is common, sparking into existence quickly anywhere in the universe.
A NASA astrobiologist, Abigail Allwood, hoped it was true, but she wanted to take a look for herself. In September of 2016 she and her colleagues traveled to Greenland.
This month they published a rebuttal of the previous study in the journal Nature.
Allwood and her colleagues say the Greenland structures do not have a biological origin. They’re just rocks.
The “conical” structures previously identified as fossilized stromatolites aren’t truly conical, the new report states. The authors say they’re the cross-section of what is a ridge, an elongated structure formed through natural tectonic forces. “They’re not ice cream cones. They’re Toblerone bars,” said Allwood, who works at the NASA Jet Propulsion Laboratory in Pasadena, Calif.
The lead author of the 2016 paper, Allen Nutman, a geologist at the University of Wollongong in Australia, said he and his co-authors are “mystified” by the Allwood report and stand by their earlier interpretation.
The new report is the latest eruption of contentiousness in paleobiology, which has long been marked by disagreements over what’s a fossil and what’s just a bit of interesting geology.
The age of the Greenland site is not in dispute. It is possible that there are relics of early life in the formation. But the burden of proof is on Nutman, said Roger Buick, a University of Washington scientist who two years ago expressed skepticism about the 2016 report.