Rocks found to contain structures that may have been created by microbes 3.7 billion years ago.
In the ancient rocks of Greenland’s southwest coast, scientists writing in the journal Nature have discovered what they believe to be the world’s oldest fossils.
It was four years ago that a team of Australian and British scientists came across the stromatolites — layered mounds of sediment built by microbe colonies that thrive in shallow waters — rising out of the flat rock. At 3.7 billion years old, these newly found fossils are 220 million years older than the previous record holder for the oldest remnants of life on Earth.
Yet the researchers waited until now to publish their significant discovery. “Of course one felt very excited, but we’re not the rushing types and we took our time,” team leader Allen Nutman of the University of Wollongong in Australia tells The New York Times. “We kept it secret because we wanted to present it in the most robust way we could manage.”
Those same rocks on the Isua supracrustal belt of Greenland — the world’s oldest known rocks — had previously yielded only indirect evidence of life, in the form of carbon and sulfur isotopes that may have been produced by ancient microbes. The stromatolites are the first potential pieces of direct evidence of these earliest life forms on Earth.
But having been around for billions of years, the rocks in which the fossils were found have been exposed to extreme conditions. Heat and pressure have transformed them, and in doing so, many of the hallmarks normally used to identify stromatolites were no longer observable.
"It's remarkable that they have found [the structures], and they've done a good job of analyzing what's there,” Abigail Allwood, a geologist with NASA’s Jet Propulsion Laboratory in Pasadena, California, who was not involved in the study, tells Live Science. “But the alteration that the rocks have seen means that there's just a whole lot of stuff that you'd typically like to see to make such an extraordinary claim, that just isn't preserved.”
If the microbial origin of the structures are confirmed, they will represent the oldest remnants of life, having arisen when our 4.5 billion-year-old planet was still in its infancy.
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