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article imageRemnants of Earth's 4.2 billion-year-old crust found in Canada

By Karen Graham     Mar 19, 2017 in Science
Two geologists studying some of North America's oldest rocks have uncovered ancient minerals that are remnants of the Earth's original crust that formed over 4.2 billion years ago.
Canada is already home to a vast treasure-trove of artifacts relating to the formation and ultimate progression of life on Earth, from the finding of 200-million-year-old bone fragments dating to the early Jurassic period on the shores of the Bay of Fundy, to the oldest archaeological evidence pointing to the earliest traces of human migration across the Beringia land mass in the Yukon.
Jonathan O’Neil and Richard Carlson were on a trek to the northeastern part of Canada to study the Canadian Shield formation. It's a rather large region of exposed continental crust, underlying and centering on the Hudson Bay. This area is already known to contain some of the oldest parts of North America, according to PBS.
The discovery  on the Eastern shores of the Hudson Bay in northern Quebec  gives scientists an unpre...
The discovery, on the Eastern shores of the Hudson Bay in northern Quebec, gives scientists an unprecedented insight into how the Earth was formed.
The continental crust remnants in what is called the Canadian Shield are known to be around 2.7 billion years old. But it is the much older crust, from around 4.7 billion years ago that has remained elusive. And that is exactly why O'Neill and Carlson made the trip to Northern Quebec, hoping to find samples.
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The vast majority of the Earth's rock record and crustal formations has been destroyed because the planet's crust are always moving. This motion creates subduction and a recycling of the surface crust back into the mantle, something that is not seen in other known planets or the moon.
And while there are a few slivers here and there of 4-billion year-old crust remaining, only isolated zircon mineral grains are dated to be older, according to the research paper published by O'Neill and Carlson in the Journal Science on March 17, 2017, that announced their find.
Jonathan O Neil  of McGill University in Montreal and Dr Richard Carlson  from the Carnegie Institut...
Jonathan O'Neil, of McGill University in Montreal and Dr Richard Carlson, from the Carnegie Institution for Science in Washington DC, led the study.
O’Neil is an assistant professor of geology at the University of Ottawa, and he likens rocks to books. The composition of rocks tells a story of the conditions that existed when they were formed. However, he says the first billion years or so of Earth's history is nearly completely unrepresented.
“We’re missing basically all the crust that was present about 4.4 billion years ago. The question we’re after with our study is: what happened to it?” said Carlson, the director of the Carnegie Institution of Washington. “Part of the goal of this was simply to see how much crust was present before and see what that material was.”
The two geologists talked about the "parentage" of rocks, explaining that rocks all have a precursor or parent. But O'Neill says that just how old was something they didn't know.
There is one way to date rocks, and that's by measuring an isotope that was only produced within the Earth's first 500 million years, neodymium-142 which the team found in the Quebec samples.
Close-up of 2.7 billion-year-old continental crust from Nunavik  northern Quebec showing a complex h...
Close-up of 2.7 billion-year-old continental crust from Nunavik, northern Quebec showing a complex history of re-melting of oceanic-type rocks that were older than 4.2 billion years. (Véronique Villeneuve)
The measurements made by the team determined the rock samples they found formed between 4.2 billion and 4.3 billion years ago. And while this new knowledge doesn't give us complete insight into the formation of the Earth's original crust, it does give us some new questions that need answering, reports CBC Canada.
"At least it gives us more tools to understand the early geodynamics," O'Neil said. "Was [the process] the same everywhere on Earth? Or was it local? These are all questions we'll have to answer. If we understand early processes that shape our planet, we can maybe understand other planets: Why are they different? Or are they similar and where in their life did they drift apart in terms of geology?"
More about Earth's original crust, canadian shield, zircon mineral, Quebec, continental crust
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