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A Buddhist monk is trekking through the mountainous terrain of the Tibetan Plateau. At an altitude of more than 10,000 feet, he eventually comes to the opening of a curious cave. Here, he finds what appears to be the ancient remains of a jaw. The monk picks up the bone and determines to pass it on to someone with expertise in archaeology. And it’s a good job he did. After all, his find will one day shed light on a special genetic trait of the Tibetan people that has long baffled scientists.

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It was only 30 years after the jawbone’s discovery, however, that the find was subjected to the level of scientific scrutiny that it deserved. In 2010, in fact, Dongju Zhang turned her attention to the object. Having just completed her Ph.D., the researcher was unsurprisingly eager to get stuck into the work.

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Zhang wasn’t acting alone, however. She’d initially taken an interest in the bone thanks to a push from her academic mentor, Fahu Chen. And it was Chen himself who headed up the research, which involved several experts in addition to Zhang. All these people’s work ultimately culminated in a study that was published in May 2019.

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Essentially, then, it’s taken almost four decades since the bone’s discovery for its true significance to start to be recognized. But with this piece of research from 2019, the scientific community has a compelling new idea over which to pore. It revolves around a potential connection between this ancient jawbone and an evolutionary adaptation seen today in the people of Tibet.

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For those who don’t know, the region of Tibet is situated in Asia. It encompasses most of the Tibetan Plateau, a significant expanse of highland that spreads across roughly 970,000 square miles. For a sense of scale, we can say that the plateau is about five times larger than France. It reaches into parts of both China and India, too.

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Tibet is considered to be the loftiest place in the world as well. On average, you see, the land tends to stretch to about 16,000 feet into the sky. Having said that, the region’s most significant point is much higher. This is Mount Everest – the tallest mountain in the world – which reaches a height of more than 29,000 feet.

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Over the years, of course, archaeologists have attempted to piece together the earlier stages of Tibet’s history. Certain pieces of evidence have indicated that species of humans were present in the region roughly 500,000 years ago, for instance. But modern humans seem to have shown up much later – about 21,000 years ago.

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Nowadays, though, the number of Tibetan people isn’t known precisely. The population is no longer focused specifically in Tibet, you see, with some being located in other parts of China. Tibetans also inhabit India, Bhutan and Nepal as well as other, more faraway parts of Earth. Yet a figure of 6.5 million has been posited.

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The Tibetan people communicate in a variety of different tongues, too. Some of these languages can even be so distinct that they’re essentially incomprehensible to one another. Yet in terms of religion, the majority of Tibetans are Buddhists – though a native religion known as Bon has also survived among some. Islam is practiced by a minority as well.

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Genetically speaking, though, Tibetans today share many of the same characteristics and traits as other peoples of East and Central Asia. Yet they’re unique in that they can live at significant altitudes that other people cannot. This is a fascinating quality of the Tibetan people – and one upon which Fahu Chen’s 2019 study might shed light.

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As we’ve heard, the jawbone – or mandible, as lower jaws are also known – at the center of this study was found at the Baishiya Karst Cave. This is a sacred Buddhist site that attracts pilgrims and monks. It was here, in 1980, that an unnamed monk came across the ancient jaw. The relic is now referred to as the Xiahe mandible. It acquired this moniker as a reference to the county in which the jawbone was found.

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So the monk later brought the Xiahe mandible to a significant individual within the Buddhist faith. After that, the find eventually ended up at China’s Lanzhou University – where it lay in relative obscurity for quite some time. In 2010, however, Dongju Zhang – with encouragement from supervisor Fahu Chen – took an interest in it.

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What’s so special about the Xiahe mandible? Well, attached to the jawbone are a pair of big teeth – quite unlike what you’d expect to see in modern humans. It also appears to be without a chin, a feature that is specific to our species. All of this was rather telling for researchers, then. Had the mandible once belonged to another species of humans?

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In search of an answer, scientists tried to retrieve DNA from the mandible. When this proved unsuccessful, however, the experts attempted to study the proteins which lay within it. They then noted that the jawbone exhibited characteristics suggestive of a recently classified species of human known as the Denisovan.

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In fact, the Denisovan species was only identified in 2008. That’s because a finger was found in a Siberian cavern known as Denisova Cave. And over the next couple of years, the specimen was subjected to much testing. And while the digit exhibited similarities to the Neanderthal, it appeared to be different in other ways. The bone was therefore proclaimed to have belonged to a new species of human.

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According to a paleoanthropologist named Bence Viola, the Xiahe mandible is what one would expect from a Denisovan specimen as well. “To me, it hits the expected morphology really well,” the specialist from the University of Toronto told National Geographic magazine in 2019. “It really looks like what one would have hoped for.”

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So while the Denisova Cave fossil was the first Denisovan bone to be officially classified as such, it was the Xiahe mandible that had been discovered first. After all, the jawbone was found 28 years before the finger. It just so happened that nobody realized the body part’s significance for quite some time.

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When they eventually started working on the Xiahe mandible, though, the researchers from Lanzhou University sought to establish how old it was. To do so, they analyzed the rock within which the bone had been found. The experts concluded from this that the mandible dated back about 160,000 years – an age comparable to the Denisova Cave discovery.

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If this date is correct, it implies that Denisovans were found in Tibet well before modern humans ever showed up. To be more precise, it seems that there was a period of about 120,000 years before our species joined the Denisovans there. And that’s not all that the Xiahe mandible can tell us.

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Before the Xiahe mandible had been classified, the only other evidence of the Denisovans came from the Siberian Denisova Cave. Baishiya Karst Cave is, however, over 1,400 miles away from Denisova Cave. This tells us that Denisovans were living in other parts of Asia than had initially been comprehended by experts.

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The discovery also implies that Denisovans were capable of living at notably high altitudes. After all, the Baishiya Karst Cave in which the Xiahe mandible was discovered is more than 10,700 feet above sea level. It’s said that weather conditions in the time of the Denisovans could have become extremely cold, too – perhaps around -22 °F at times.

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The fact that there’s evidence indicating Denisovans’ ability to survive in extreme conditions could have significant implications. You see, most modern humans are unable to live at great heights. That’s because up high – where there’s less oxygen – the human body produces a higher quantity of a protein known as hemoglobin.

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Hemoglobin is useful in that it allows oxygen to be transported around the body more effectively. However, if our bodies are exposed to too much, the protein can interfere with the workings of the heart. This might cause the onset of altitude sickness or even bring on a heart attack – which could prove deadly.

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This is the case for most people on Earth. The Tibetan people, however, don’t necessarily produce too much hemoglobin in these conditions. The reason for this is down to EPAS1 – a special gene that has been nicknamed the “super-athlete gene.” That’s because it ensures the body uses its oxygen more adeptly.

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But how exactly is it that the Tibetan people have managed to come by this handy gene? Well, the answer, it seems, could be indicated by the Xiahe mandible. It all has to do with the fact that early species of humans were known to interbreed with one another. In doing so, they would have exchanged certain genetic traits.

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Modern humans are thought to have derived from Africa, for instance. However, about 200,000 years ago, they started migrating to other parts of the world. And at some point, they made it to the Middle East – where they came across and mated with Neanderthals. Yet others traveled to Asia and bred with Denisovans.

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The resulting offspring from these encounters would’ve been born with genetic traits taken from each of these species. And evidence of this can be seen in the Tibetan people today. The EPAS1 gene is, for instance, thought to trace back to the Denisovans. At one time, though, it appeared that this gene came into being for reasons that did not concern altitude.

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In fact, experts once believed that EPAS1 had emerged in Denisovans to help them handle intensive exercise. Then, it was thought, the gene was later utilized for other functions. But the Xiahe mandible suggests that Denisovans lived in areas defined by great heights. So it seems that the gene emerged to cope with these significant altitudes.

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As the head of the Spanish National Research Center on Human Evolution, María Martinón-Torres is undoubtedly an authority on matters of this nature. And in an email to National Geographic, she proclaimed that the Xiahe mandible has been influential in detailing the Denisovans. As she put it, “Thanks to this study, we are ‘cornering’ Denisovan. Their portrait is progressively less blurred.”

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The notion that the Tibetan people of today can trace their ability to live in high altitudes to the Denisovans isn’t exactly new, though. In fact, a piece of research published in 2014 already argued such a thing. Now, then, the Xiahe mandible appears to back up the claims of this other work.

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Yet things aren’t quite so straightforward. There are, in fact, those who are cautious to subscribe to these new theories. One example is Emilia Huerta-Sanchez, a genetics expert from Brown University. “I agree with the authors [of the 2019 study] that it could be that this hominin group [the Denisovan] was high-altitude adapted,” the Rhode Island-based academic stated. “But I don’t think we know for certain.”

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As we saw earlier, the researchers working on the Xiahe mandible failed to extract DNA from the specimen. So, Huerta-Sanchez argues, we can’t be certain that the individual to which it once belonged did possess the genetic trait to help it survive at high altitudes. Yet while she’s expressed doubt that this is the case, it does appear that Huerta-Sanchez wishes it to be so.

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But there are other reasons to be skeptical of such claims. You see, it’s thought that the Denisovans were an incredibly diverse species. Another study from 2019 has posited that what we call Denisovans can be split into three different categories, which themselves are incredibly divergent from one another. This calls into question the very notion of the Denisovan as a specific species.

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Yet even though doubts exist, the new way to study fossilized proteins and reveal new information is in and of itself exciting to experts. As Martinón-Torres elaborated to National Geographic, “I love the way cutting-edge techniques have been put together to make the dead speak. Paleo-genetics was a revolution in the paleoanthropological field and now proteomics constitutes another frontier [of] research, opening a door to unforeseen dimensions of knowledge.”

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Of course, some questions remain unanswered about the Xiahe mandible. Yet the jawbone could prove useful to scientists down the line. For instance, new fossils discovered throughout Asia may be compared to it. And those bones might subsequently be identified as having belonged to a Denisovan as well.

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And on top of everything else, the Xiahe mandible has shown that there are potential anthropological treasures to be discovered up high. As paleoanthropologist Viola pointed out to National Geographic, “The high mountains of Asia are really, really unknown. People usually just assumed nobody lived there.”

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Viola is himself researching a lofty site thought to have once housed ancient species of human. This is Kyrgyzstan’s Sel’ungur Cave, which is situated about 6,200 feet above sea level. Viola and his colleagues initially thought that this place had accommodated Neanderthals – but the Xiahe mandible research has suggested an alternative. As he put it, “Maybe they were Denisovans.”

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So the Xiahe mandible may completely upend previous notions related to early human species. Indeed, these are the thoughts of one of the experts involved in putting together the 2019 paper. As Jean-Jacques Hublin proclaimed to The Guardian, “Until today, nobody imagined that archaic humans could be able to dwell in such an environment.”

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The Baishiya Karst Cave itself might yet inform scientists even further. In addition to the Denisovan jawbone, you see, other skeletal remains have been found inside. These seemingly belonged to different animals, and they were discovered alongside what appear to be tools. It remains to be seen if these things can be linked to the Denisovans, though.

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Yet, whatever the case may prove to be down the line, the research centered on the Xiahe mandible has already been celebrated as groundbreaking. The very fact that it utilized protein testing to identify an ancient human species is itself significant. Perhaps using similar methods in the future will help to classify all sorts of fossils littered around China today.

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And remains can crop up anywhere. In April 2019 the world watched in horror as flames engulfed one of Europe’s most iconic buildings, leaving little more than a charred and broken ruin. But fast forward one year, and experts are hard at work renovating the gothic beams and arches of Notre-Dame de Paris. In amidst the piles of ash and debris in the cathedral, however, a scientist made a somewhat disturbing discovery.

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In order to understand the gravity of the situation, though, let’s recap the horrifying events of last year. The first sign that something was amiss came in the early evening of April 15, 2019, when an alarm notified staff of a fire somewhere in the famous cathedral. After evacuating the building, they rushed to put out the blaze – only to find that they weren’t in the right place. And when they finally reached the correct spot, the flames had, unfortunately, already taken hold.

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For those in charge of looking after the cathedral, it was a disaster that they’d long feared. With parts of this vast structure dating back to the 12th century, the precarious state of its stonework was already extremely vulnerable. And in the attic and spire, oak beams from the 1200s had dried out, posing a worrisome fire risk.

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In fact, by April 2019 Notre-Dame was being monitored by fire wardens on several occasions each day. Sadly, however, that didn’t stop a blaze from breaking out, probably as a result of an electrical issue. And for more than three hours, Parisians looked on in shock as flames tore through the roof of the historic cathedral.

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During the blaze, hundreds of firefighters worked tirelessly to extinguish the flames. And in the meantime, the emergency services formed a human chain to remove priceless artifacts from the terrifying inferno. By the time that the fire was put out, however, the iconic building was a mere shadow of its former self.

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When the sun rose the next morning, then, it illuminated a damaged and broken Notre-Dame. In the fire, some two-thirds of the cathedral’s roof had been destroyed, and its 19th-century spire had fallen. Moreover, as it tumbled down, it pierced the ceiling of the vault below, which catastrophically exposed the building’s interior to the burning wreckage.

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As the citizens of Paris grieved, news outlets across the globe broke the story of the staggering loss. Reporters also clamored to find out the fate of the priceless artifacts that the cathedral had held in its walls. Which among them had been saved from the fire – and which had been destroyed by the relentless flames?

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At the time, you see, Notre-Dame had housed many important religious artifacts, such as a crown of thorns purported to have been worn by Jesus Christ. Additionally, the cathedral also held a piece of ancient wood that was said to have come from the cross used at the Crucifixion. But it wasn’t only objects associated with Christianity that were in peril as the building burned.

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That’s right: onlookers also feared for the fate of Notre-Dame’s 18th-century organ, which is so revered that musicians have to register with the cathedral years in advance just for a chance to play it. And what of the countless statues, some of which dated back to the 1300s? Or the famous Mays paintings, gifted to the cathedral annually between 1630 and 1707?

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Thankfully, the worst-case scenario didn’t materialize. In fact, some of Notre-Dame’s most famous pieces of art weren’t even in the building at the time that the fire broke out. Towards the end of 2018 repair work had commenced at the cathedral, and as a result, a number of items had been taken from the vault for safekeeping.

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Yes, many of Notre-Dame’s religious treasures were stored within the sacristy – a nearby building that wasn’t damaged in the blaze. And as for the artifacts that were within the burning cathedral, many were saved by rescue workers. Not all of the masterpieces of this beloved landmark could be saved, however.

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“We have avoided a complete disaster,” the Observatory for Religious Heritage’s Maxime Cumunel told Reuters in 2019. “But some five to 10 percent of the artwork has probably been destroyed, [and] we have to face up to that.” And as smoke-damaged paintings were removed from the cathedral’s blackened ruins, the grave reality of the situation began to hit home.

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In the days and weeks following the fire, a number of companies and individuals came forwards with generous donations to help pay for the restoration of Notre-Dame. The French businessman Bernard Arnault, for example, gave the equivalent of $200 million to the cause. However, experts believed that renovation work could cost several billion dollars.

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In the meantime, then, restoration experts began to pick their way through the shell of Notre-Dame, clad in helmets to protect against falling debris. While the ruins still smoldered, French President Emmanuel Macron had promised the world that the icon church would be reconstructed. And now, it was the task of these experts to work out how.

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At first, these specialists were comforted by how many of the cathedral’s relics had been spared. In a 2020 interview with Science magazine, Aline Magnien from the Historical Monuments Research Laboratory, or LRMH, explained. “What matters isn’t the roof and vault so much as the sanctuary they protect,” she said. “The heart of Notre-Dame has been saved.”

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Nevertheless, the restoration looks set to be a mammoth undertaking. For Magnien’s team at LRMH, the first task has been to try to stop any additional destruction from taking place. Then, the 23-strong group hopes to use its research to instruct constructors on how best to rebuild the church.

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There have been many hurdles for the team to conquer along the way, however – and it looks as though there will be more to come. For example, one of the first problems that researchers encountered was reaching the cathedral’s damaged stonework. Climbing onto the top of the vault, they reasoned, could cause the entire structure to collapse. But at the same time, observing it from underneath would put them at risk from tumbling detritus.

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So researchers have been unable to determine just how unstable the ruins of Notre-Dame really are. Nonetheless, they’ve found that analyzing the color of the stonework has delivered some surprisingly useful results. According to the experts, you see, limestone blocks take on a different hue depending on the temperatures that they have been exposed to.

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At between 570°F and 750°F, for example, the iron inside the limestone decomposes, leaving behind a layer of red. And as temperatures rise even further, the color shifts to black. Ultimately, at around 1,500°F, the blocks are little more than powder. Armed with this knowledge, then, researchers have been able to determine the sturdiness of individual stones simply by evaluating their color.

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Another issue for researchers has been the amount of water that has made its way into the ruins of Notre-Dame. During the blaze, it seems, firefighters were instructed to aim their water jets away from the fragile stained-glass windows. However, they couldn’t do the same for the stone vault, as the flames threatened to engulf it.

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As the firefighters turned their hoses on the limestone walls of the cathedral, the porous material absorbed the water – drastically increasing its weight in some instances. And almost a year later, researchers have noted that it still hasn’t completely dried out. What’s more, the water in the stones expands and contracts depending on the temperature, further wreaking havoc with the unstable structure.

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Today, work to protect the fragile shell of Notre-Dame and to restore it to its former glory continues. Macron, you see, has promised that the cathedral will be ready for the public to enter as early as 2024. In the meantime, though, researchers have been enjoying a unique insight into the now-blackened landmark that’s defined Paris for hundreds of years.

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Philippe Dillmann, a metal specialist working with LRMH, told Science magazine, “We’re sorting these thousands of fragments – some from our world, some from another and more ancient world. And it’s like we’re communicating with the Middle Ages,” Elsewhere, experts have been seizing the opportunity to deduce the techniques of the 13th-century stonemasons who built the cathedral.

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In fact, even the loss of Notre-Dame’s great attic hasn’t been completely without a silver lining. According to experts, an analysis of the remaining beams suggests that they were grown-to-order in a dedicated forest. And given the age of the wood, this implies that the construction of the cathedral was intended for at least a century prior to building work commencing.

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But while it might seem that Notre-Dame itself had a somewhat lucky escape, the citizens of Paris have perhaps not been quite so fortunate. Apparently, while the roof of the cathedral burned, great quantities of poisonous lead melted and were released into the atmosphere. Shockingly, though, it has yet to be traced.

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Even today, lead is present in roofs across the planet. However, it can also be toxic, with exposure to it sometimes resulting in a number of physical and neurological problems. As well as behavioral difficulties, for instance, it’s believed that the substance can also lead to conditions such as infertility, seizures and even death.

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In the aftermath of the Notre-Dame fire, many Parisians grew concerned that lead from the roof may have contaminated the areas surrounding the cathedral. At first, though, the science seemed reassuring. According to metallurgist Aurélia Azéma, a section chief at LRMH, the blaze didn’t reach the temperatures necessary for reducing the material to gas.

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Moreover, much of the melted lead from the roof clearly remained in the cathedral, where it solidified to form stalactites. And as officials declined to issue public warnings about the issue, many residents might have assumed that they were safe. However, a far more sinister story was playing out behind the scenes.

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Some witnesses, you see, had spotted a yellow haze forming over Notre-Dame as the fire raged below. And according to some of the experts, the inferno did, in fact, exceed the temperatures at which lead combines with oxygen, essentially creating an aerosol effect. So, it seems clear that a portion of the toxic material did find its way into the atmosphere around Paris.

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But where did it go? Worryingly, authorities didn’t test the neighborhoods close to the cathedral for several weeks. And when they did, they discovered that a number of local schools contained significant levels of lead. Some recreational areas returned readings of more than 60 times the recommended limit, too.

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Because of lead’s toxic nature, French law states that only trace amounts of the substance are allowed on buildings. There have been rumors, however, that officials have attempted to cover up the dangerous levels released by the Notre-Dame fire. Indeed, a 2019 report by The New York Times claims that the risk was known within a couple of days of the disaster – but authorities failed to act.

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In September 2019, representatives from Robin Hood, an environmental organization based in France, announced some worrying news. The residents of an apartment one mile from Notre-Dame had asked for some lead tests to be conducted at their property. And on the balcony, experts had found levels of around 20 times the recommended limit.

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In addition, lead content eight times the legal limit was detected at a Paris police station. And in a 2019 interview with The Daily Telegraph, union representative Frédéric Guillo explained his concerns. He said, “It proves once again that the lead contamination caused by Notre-Dame fire is a serious, long-term problem that authorities need to protect their citizens from.”

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But while the people of Paris are rightly concerned about the lead drifting around in their atmosphere, Notre-Dame itself remains ground zero for this toxic leak. In fact, Azéma detected traces of the material throughout the cathedral – even inside the pipes of an organ. And elsewhere in the building, another scientist made an alarming discovery.

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In the ruins of Notre-Dame, wood specialist Emmanuel Maurin, who also leads a team at LRMH, ran tests on surfaces made from oak and other materials. And when he looked at the results, he discovered levels of lead at around 70 times the recommended limit. Despite this, however, those working in the cathedral in the months after the fire weren’t even equipped with proper precautionary clothing.

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Thankfully, by March 2020, all that had changed. Researchers working at Notre-Dame were now obliged to submit to rigorous decontamination procedures. According to reports, they’re limited to two and a half hours inside the ruins, after which they must throw away their disposable garments. The scientists are then required to take a thorough shower, a task that they sometimes complete up to five times a day.

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Although researchers must follow these strict guidelines, there are some who believe that Notre-Dame might have been releasing toxic lead into the environment for years. Even before the fire, for example, it’s thought that rainwater may have washed the material from the roof into the nearby River Seine. And as a result, it could have already been contaminating the region for hundreds of years.

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What’s more, there are other factors that could be affecting lead levels across Paris, including the use of gasoline and toxic paints. So, exactly how much of it can be traced back to the fire at Notre-Dame? In an attempt to solve the mystery, then, scientist Sophie Ayrault plans to compare samples taken at the cathedral to those gathered elsewhere in Paris. This vital work has yet to take place, however.

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In the meantime, the team at LRMH have been busy trying to find ways of removing lead traces from the ruins of Notre-Dame. So far, ideas have included using a special putty to extract the toxic material and deploying lasers to cleanse the porous stones. But according to geologist Véronique Vergès-Belmin, who heads up the LRMH’s stone department, the process will likely involve a series of different approaches.

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Still, as The Guardian reported back in April 2019, Macron promised that Notre-Dame would be rebuilt “more beautiful than before.” And now, researchers at LRHM are echoing this sentiment. Speaking to Science magazine, Magnien claimed, “Notre-Dame will come out of this experience enriched. And so will we.” But if it can be proven that toxic lead has leaked from the cathedral into Paris’ parks and schools, it seems likely that the fire will leave behind a far darker legacy.

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