In August 2016, a research team claimed to have unearthed evidence of life in a remote outcrop of 3.7-billion-year-old rocks in Greenland. This bold claim not only pushed back the origin of life by at least 220 million years, it also added to a growing body of evidence that challenged the standard story of Earth’s violent beginning, as Quanta Magazine reported this year in “Fossil Discoveries Challenge Ideas About Earth’s Start.” Joining a series of ancient fossil finds—as well as geological evidence from Earth and the moon—the Greenland discovery added weight to the idea that Earth was warm and watery from the outset, and that in such conditions, life emerged quickly.

But a follow-up study published in Nature last week makes the case that those Greenlandian signs of life may just be a case of squished rock and mistaken identity. In it, the authors argue that the geologic features that were taken as clear marks of life can be readily explained by the normal, lifeless workings of tectonic forces. The debate highlights the challenges in reading signs of life into relics.

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