Until now, the oldest known stromatolites came from Western Australia, and were 3.48 billion years old. They represented the earliest convincing evidence of life on Earth. And the structures that Nutman, Bennett, and Friend discovered in Greenland are 3.7 billion years old—220 million years older than the Australian ones. If the trio are reading them correctly, and they really were produced by bacteria, then they are easily the oldest fossils ever found.

If you condense the entire history of the Earth into a single calendar year, then the bacteria that created the Greenland fossils were alive in the second week of March. And since they were already sophisticated, capable of forming large colonies, life itself must have arisen much earlier, perhaps sometime in mid-February.

The implication is that once the Earth was born, it didn’t take long for life to get going. As NASA geologist Abigail Allwood writes in an accompanying commentary, “The cradle of life [might have been] ready and rocking when Earth itself was but an infant.”

Stromatolites have long been controversial. Natural processes can produce structures that look very similar to stromatolites, and many scientists have become embroiled in long debates about whether a given bit of rock was really the work of microbes. Regardless, it’s commonly accepted that the oldest known stromatolites are from the Pilbara region of Western Australia, and are 3.5 billion years old.

Stromatolites in Australia. Credit: Paul Morris

It seemed unlikely that researchers would find older ones, given that there are few other sites on Earth where older rocks actually exist. Western Greenland—and especially a coastal site called the Isua Greenstone Belt—is an exception, but still a problematic one. Its rocks are certainly ancient, but they’ve also been put through the wringer, warped and distorted by intense heat and pressure. They seemed unlikely to preserve the clean layers and shapes that make stromatolites so distinctive.

At first, Nutman and others searched the Greenland rocks for alternative signs, like chemical signatures that could betray the activity of living things. They found a few such signatures, but none made for a slam-dunk case. “The chemical evidence could be interpreted as signs of life, but there’s always been some element of doubt,” says Nutman. “But what we have now is something very different—something tangible and visible you can see, rather than a reading that’s come out of an instrument.”

His team found what they think are stromatolites in three separate outcrops. These patches of rock are small, and like everything else in the region, they’ve been heavily distorted. Still, the team managed to check off a long checklist of criteria that they think firmly identify them as stromatolites. For example, there’s their shape—steep-sided cones or domes that look very much like the Pilbara stromatolites and unlike any structures formed through physical processes alone. These shapes represent stromatolites poking out of shallow water, as sand piles up against their sides.