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Yahoo
a day ago
- Science
- Yahoo
A Fragment of Earth's Original Crust Still Exists—and It's Buried in Canada
"Hearst Magazines and Yahoo may earn commission or revenue on some items through these links." Here's what you'll learn in this story: What are now thought to be the oldest rocks on Earth have been confirmed to have an age of almost 4.2 billion years, almost as old as the planet itself. Researchers were met with controversy for their initial claims, but dating isotopes of one metal that decayed into another showed that the igneous rock from northeastern Canada really was that old. This ancient piece of our planet could tell us more about its turbulent past. Earth is about 4.5 billion years old, and as the eons passed, the crust of the young planet experienced turbulence. Asteroid collisions shattered some parts, which melted and recrystallized, while tectonic plates constantly shifted and triggered volcanic eruptions that oozed magma over the surface. Erosion further erased evidence of our planet's early scars. The most ancient layers of crust were all but lost—until now. The oldest crust on our planet formed during what is known as the Hadean epoch. Reaching back to the period between 4.6 to 4 billion ago, this was when the Solar System was still forming in a thick haze of gas and dust (possibly the refuse from a supernova) that surrounded the nascent Sun. It is an epoch not even considered part of geologic time because, for years, the only rocks found dating back from this period were meteorites that fell from space. Hadean meteorites and lunar rocks up to 4.5 billion years old have been found before, but nothing directly from Earth even came close. As Earth became covered in swaths of ocean, layers of soil and landscapes as diverse as forests, deserts, mountains, volcanic plains, glaciers, grasslands and cities built by humans, primordial relics were buried even deeper. Anything found to have been part of our planet's crust in the distant past was 3.8 billion years old or younger. That puts even our latest findings in the Archean period, which followed the Hadean. Geologist Jonathan O'Neil of Ottawa University in Canada refused to believe there were no Hadean fragments of crust remaining. While zircons found embedded in Australian rocks were successfully dated back to that period, an actual piece of crust that old had never surfaced. In a controversial 2008 study, O'Neil and his research team claimed that they had discovered a part of the original crust in northeast Canada's remote Nuvvuagittuq Greenstone Belt. This formation has stayed intact almost since Earth was born. It could be a portal into Earth's earliest growing pains. There was just one problem. Another group of researchers steadfastly argued that the rocks of the Nuvvuagittuq Greenstone Belt were no older than 3.8 billion years. While the 4-billion-year-old rocks of the Acasta gneiss in the northwest of Canada were slightly older, having just barely formed at the end of the Hadean, they were still not old enough. O'Neil was determined to prove that the Nuvvuagittuq rock, originally a flood plain of magma that hardened into volcanic basalt, predated the other pieces of crust. It turned out that the evidence was hiding in the rock itself, and not in the form of zircons. When they first formed, they had contained samarium, a metal which oxidizes when exposed to air. Any samarium in the rocks was long gone. However, samarium isotopes had left behind chemical signatures of their decay into isotopes of neodymium. Two different isotopes of neodymium which had come from two samarium isotopes were both dated to 4.16 billion years. 'The age agreement between both extant and extinct radiogenic systems, in rocks related through igneous fractionation, is compelling evidence for preservation of Hadean rocks in the Nuvvuagittuq Greenstone Belt, opening a rare window into Earth's earliest times,' O'Neil and his colleagues said in a study recently published in Science. There could be more crust that ancient which has not been unearthed yet. It is even possible that some may have landed on the Moon. 4.4 billion years ago, not long after Earth formed, an extreme collision shattered part of the Earth and formed our only satellite, which has not been explored by humans since the Apollo Era. What future Artemis astronauts find once we return to the Moon might give us more insight about how our planet grew up. You Might Also Like The Do's and Don'ts of Using Painter's Tape The Best Portable BBQ Grills for Cooking Anywhere Can a Smart Watch Prolong Your Life?
Scientific American
4 days ago
- Science
- Scientific American
Rocks in Canada Are Confirmed as World's Oldest
3 min read In 2008 scientists reported that rocks in Canada were the world's oldest. New data appear to confirm this contested claim By & Nature magazine On the shores of Hudson Bay in northeastern Canada lie what could be the world's oldest rocks. A study now suggests they are at least 4.16 billion years old — 160 million years older than any others recorded, and the only piece of Earth's crust known to have survived from the planet's earliest eon. In 2008, researchers reported that these rocks dated back 4.3 billion years, a claim that other scientists contested. Work reported today in Science 1 seems to confirm that the rocks, known as the Nuvvuagittuq Greenstone Belt, are record-breakers. Researchers say the rock formation offers a unique window into early Earth, after the planet cooled from its fiery birth 4.5 billion years ago. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. 'It's not a matter of 'my rock is older than yours',' says Jonathan O'Neil, a geologist at Ottawa University who leads the research team. 'It's just that this is a unique opportunity to understand what was going on during that time.' The 'oldest rocks' label has sometimes backfired. In the past few years, other teams have chiselled many samples out of the Nuvvuagittuq belt, leaving the landscape scarred. Last year, the local Inuit community closed access to the rocks to prevent further despoliation. Only a handful of geological samples in the world date back to 3.8 billion years or older. Of those, the oldest undisputed rocks are found in the Acasta gneiss formation in Canada's Northwest Territories; at 4 billion years old, they mark the boundary between Earth's first geological eon, the Hadean, and the following one, the Archaean. Geologists have also found tiny mineral crystals dating back to the Hadean — such as 4.4-billion-year-old zircon crystals from Western Australia — that have become embedded into newer rock. But there are no known surviving chunks of crust from the Hadean — except, perhaps, the Nuvvuagittuq Greenstone Belt. It consists primarily of material that started out as volcanic basalt before undergoing various modifications during Earth's tortured history. In their 2008 work, O'Neil and his colleagues analysed the chemical imprint left by the radioactive decay of the isotope samarium-146 into neodymium-142 to calculate that the Nuvvuagittuq rocks were 4.3 billion years old. (Samarium-146 is a short-lived isotope that was depleted in Earth's first 500 million years, and none was left after about 4 billion years ago.) Other scientists challenged that work, arguing, for instance, that Hadean-age crust had become mixed into younger crust, contaminating the results. For the latest work, O'Neil's team analysed some once-molten rocks that had intruded into the main Nuvvuagittuq rocks like a knife cutting into a cake. By dating the intruded rocks, O'Neil and his colleagues were able to establish a minimum age for the cake itself. They used two radioactive clocks: the decay of samarium-146 into neodymium-142 and that of samarium-147 into neodymium-143. Both yielded ages of around 4.16 billion years for the intruded rocks. 'If you don't agree with this, then you need a very speculative, intricate model to get to the same answer,' says O'Neil. Having both clocks agree on an age — which wasn't the case in the earlier work — strengthens the case for a Hadean age for the rocks, says Bernard Bourdon, a geochemist at the University of Lyon in France. He remains circumspect, though, and says he would like to see additional lines of evidence, involving other radioactive isotope decays. 'I would be happy if these rocks were truly Hadean, but I think we still need to be cautious,' Bourdon says. The paper 'provides a new data set that hopefully can advance this discussion', says Richard Carlson, a geochemist at Carnegie Science in Washington DC who has collaborated with O'Neil in previous work. To Carlson, the bulk of the evidence suggests that the rocks are indeed Hadean. For now, more answers might have to wait. The Pituvik Landholding Corporation in Inukjuak, Canada — the Inuit group that is steward of the land in question — is not currently granting permits for further scientific study, due to the earlier damage by other groups. 'It's unfortunate, but I would do the same,' O'Neil says.
