About 35 kilometers south of Inukjuak, an Inuit village in the far North of Quebec, lies an unusual rocky outcrop. Known as the Nuvvuagittuq Supracrustal Belt, it's mostly made up of grey-green rock, laced with veins of red. If you took the arduous trip there, and weren't a geologist, you might not realize what you were standing on. These rocks are thought to have formed billions of years ago under a prehistoric ocean, near ancient hydrothermal vents. And now they've yielded signs of extraordinarily ancient life, rewriting our planet's history.
In a new paper in Nature, an international team of researchers say these rocks are between 3.8 and 4.3 billion years old—the oldest rocks ever found on the planet. But that's not all. Their bizarre structures are signs of the presence of ancient microorganisms, making them the oldest "microfossils" ever found, and the oldest record of life on Earth.
Our planet is just over 4.5 billion years old. Back in the era when these rocks were formed, not much more than a few hundred million years after Earth cooled and the oceans formed, it had a mostly toxic atmosphere and conditions that wouldn't be considered suitable for pretty much any sort of life we know of today. (Our planet's earliest time period, the Hadean Eon, which dated from about 4.5 to 4 billion years ago, was so hellish that it's literally named after Hades.)
That's one reason discoveries like this are important: If life could spring up on our primitive planet, chances look better that it might have emerged on other planets, too.
Geochemist Dominic Papineau, who is from Quebec, made a field expedition to the northern part of the province in 2011. It took three flights in small "propeller planes" to get to the site, he told Motherboard in an interview, as well as a three-hour boat ride.
Papineau wasn't expecting to find fossils, mostly because the rocks were all heavily metamorphosed (meaning they had undergone changes under immense pressure and heat beneath the Earth's crust, a process thought likely to destroy any possible signs of life).
So it was curious, he said, that bright red-banded iron formations were spattered among the grey-green landscape. "One hypothesis about these rocks is that there was biological involvement in their formation," said Papineau, who is a professor at University College London (UCL).
Certain types of bacteria that exist today are able to harvest nutrients from iron through a chemical reaction. Papineau began to wonder if similar organisms existed some 4 billion years ago.
"I was intrigued by the occurrence of these rocks, so I sampled them," said Papineau. "But what really gave me a hint that something important might be preserved in there is that I found concretions [mineral deposits formed by microbes] of jasper in the field."
Deposits of hematite (an iron mineral) found embedded in the quartz-like jasper formed a wide variety of structures resembling tubes and filaments, granules and rosettes. Although this implied a possible biological origin, it still wasn't a slam dunk. There are ways the structures could be created through non-biological interactions, so Papineau and the other scientists had to look further. One interesting characteristic of the formations were the layers of other minerals around them.
"The rosettes that we documented are composed of carbonate along with apatite and graphitic carbon," he said. "Carbonate with apatite is really the stuff of bones."
In other words, here was more organic matter that could have originated from microfossils.
At UCL, he and lead author Matthew Dodd used microscopy and spectroscopy to continue to investigate these rocks. Eventually, they concluded there was evidence for microfossils of ancient iron-oxidizing organisms.
There are only a few other places around the world where you can find rocks of this age.
One is the stromatolites of Greenland. In 2016, scientists announced they'd discovered fossils there dating back 3.7 billion years. At that point, they were the oldest known.
These were produced within the same geological period as those described in the new study in Quebec, and were made by oxygen-producing microorganisms. That means that not only was there life in the very early stages of the planet—it was relatively diverse.
"If there were oxygen producing microbes then, [as well as] microbes that were oxidizing iron near hydrothermal vents, we have quite a significant diversity, because these are somewhat distantly related microorganisms today," said Papineau.
The implications of finding two distinct branches of life so early in the planet's history has implications for finding life on other planets. If two separate species of bacteria were able to evolve this early on Earth, could they also be found near hydrothermal vents in Mars' ancient seas, or within Europa's possible subsurface ocean? Scientists have already found hematite concretions on Mars, in the form of "blueberries" discovered by the Opportunity rover.
Papineau choose Quebec as his target because, after learning about the work in Greenland, he knew similar samples could be found closer to home. "This is my home province. This is my home country," he said. Now, by exploring the ancient rocks of its northernmost reaches, he and his collaborators have rewritten the history of life on Earth.
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