Pratique du Shadowing: What’s Ruining Our Ruins? - Apprendre l'anglais à l'oral avec la vidéo

The United Nations has designated roughly 1,000 culturally important world heritage sites around the world.

But at many of them, something has quietly been going wrong.

Paintings are flaking away, wood is rotting, even stone is slowly dissolving into powder.

If you're wondering what's so powerful that it could take down some of our oldest and most protected sites, well, this destruction isn't the product of war or natural disasters or other huge events.

It's the work of microbes.

Here's how some mini-microbes are ruining our ruins.

First up, we're going to the Maijishan Grottoes,

a series of roughly 200 caves carved into the side of a sheer sandstone mountain in the Gansu province of northwest China.

You have to be feeling brave to cross these soaring walkways that lead inside, but once you've entered Agrano,

you can find sculptures and wall paintings from as far back as the 300s.

But despite standing through 1700 years, the site is in trouble.

In 2018, experts reported that microbial plaques had started growing on the art.

As far as we know, it's not like microbes hate art or something.

They do this to make a home for themselves or to get nutrients.

In fact, while a painting might seem like a weird place for life to grow, if you're a microbe, paintings can be full of tasty bits.

There's the paint itself, which might contain things like plant oils, egg yolk, or animal glue.

But there may also be layers of organic materials like straw or other plant fibers beneath as well,

which the ancient painters would have slathered on the wall to give themselves a smooth surface to work on.

That is a balanced meal for a microbe.

As for what kind of microbes, there's a wide variety of bacteria and algae.

Both of those organisms can do art damaging things like poop out acids or form gooey biofilms that can trap water.

You can also get molds and other fungi growing on those ruins, which spread their root-like hyphae underneath the surface looking for nutrients.

All these little fellas can physically separate the layers of a painting, causing bits to flake or fall off.

They can also cause changes in color, either by degrading existing pigments or by adding their own colors into the mix.

Green algae can turn things, well, green.

Certain bacteria can do green as well, plus yellow, brown, or black.

One kind of bacteria can even create a lovely salmon pink.

But in the case of Maijishan, there were mainly white and black splotches appearing on the walls.

When scientists analyzed the splotches, they found that a common decomposing fungus was the dominant microbe in the black biofilms.

Meanwhile, Cladosporium, a super common indoor mold, and an unclassified species of fungus were dominant in white biofilms.

As for what caused the outbreak, they don't know for sure, but it probably had to do with cave critters.

The decomposing fungus is associated with arthropods, like bugs, and fungi can also grow on animal dung or after flooding.

So animals getting into these caves to shelter from heavy rains might be contributing.

In fact, previous work on the splotches also pointed fingers at excess humidity as a possible cause

and suggested it could be from more human visitors or even shifts in the weather thanks to climate change.

We know this is possible.

The Lescaux Caves in southwestern France contain wall paintings from as far back as 22,000 years ago.

But after their rediscovery in the 1940s, lots of people began visiting, and the carbon dioxide, heat, and water vapor from their breath caused microbes to grow.

The authorities eventually closed the caves to the public, and for 40-ish years tried using biocides, including antibiotics, to get rid of those microbes.

And it worked on some of the microbes.

But that opened up space for a new fungus to move in, which left a whole new set of white stains behind.

Similar things happened when people tried to disinfect the frescoes of St. Paul in Ephesus.

So biocides don't always work as well as we hope.

Another option is manual removal, like using soft brushes, a vacuum, and a little bit of elbow grease,

which they tried in the Maijishan grottos, along with biocide treatments.

Those measures seem to have worked well, even though this is probably going to be an ongoing project.

But paintings aren't the only type of heritage under pressure for microbes.

We've also had some problems with wood.

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In the desert of New Mexico, you can find Chaco Canyon.

It's another UNESCO World Heritage Site, occupied by the ancestral Puebloan people for about 300 years, starting around the mid-800s.

While they were there, they built impressive great houses and other infrastructure out of stone and wood.

And so far, it's stood the test of time, but not entirely unscathed.

For example, in the mid-aughts, expert examined some of the wooden beams that made up the buildings and found a significant amount of damage.

Some was from weathering and other physical processes, but some was from microbes.

Now, wood, especially wood in harsh, dry environments like the New Mexico desert, can be pretty resistant to microbes like bacteria.

Wood is tough and durable because plant cells are surrounded by cell walls, and woody plants in particular pack them especially full of tough,

hard-to-break-down molecules like cellulose and lignin.

But wood is vulnerable to fungi because they have ways to get into and even get food from these compounds.

One of the main troublemakers is a group of fungi that includes brown rot fungi.

These little guys specialize in decaying the cellulose in plant cells, leaving the colorful lignin behind.

This turns the wood soft, but leaves the wood's brown color behind.

And that's where they got their name.

White rot fungi, meanwhile, turn wood white, since they decay everything, including lignin.

Some even specialize in lignin.

Another major kind of fungal wood decay is soft rot.

This looks really similar to brown rot.

In fact, it's so similar

that you generally need to look at samples under a microscope to tell soft rot and brown rot apart, even though the organisms behind the rot are pretty different.

And experts have found some brown rot and a lot of soft rot setting in at Chaco.

Some parts of the wood were so degraded they could be crushed into a fine powder with even slight pressure.

Part of the problem may have come from fissures in the wood, which can catch moisture and nutrient-rich particles from the environment, the perfect conditions for microbes to move in.

In this case, instead of biocides, we've been reburying parts of the site since the 1980s.

The idea is that digging them up likely exposed them to the moisture the fungi needed to thrive, so reburying them should hopefully remove that moisture and stop further growth.

As an added layer of protection, conservationists also installed things like moisture monitors alongside the buried material,

as well as waterproof fabric sheets or drains and pipes that can funnel surface water away from stuff buried further down.

Free burial is pretty low-tech, practical, and compared to trying to replace the wooden beams or other materials again and again, a good deal money-wise.

We like to imagine technology solving all our problems, but sometimes the best option for archaeologists is to leave things alone and preserve them for the future.

We can get the technology to fix it later.

Although eventually everything breaks down, whether it's paint or wood or even stone itself, as our last location shows.

In 2018, scientists took samples from a bunch of sites in Egypt, from tombs and obelisks to mosques and even the pyramids at Giza.

These sites are ancient and have withstood the test of time, but over the years, people have noted damage at some of them,

including black stains and pitting in the rocks themselves.

Scientists have found two species of a common mold, along with Cladosporium, one of the fungi found at Mygishan.

And we're not just seeing it in Egypt.

Another desert site, Megiddo, was surveyed in 2023.

This World Heritage site was swabbed from the visitor entrance to its major archeological sites.

Experts didn't report damage, but did detect acid producing microbes.

As for what a microbe would even want with stone, just like wood or paintings, it can give them a home and even food.

They might even damage the stone itself by doing things like dissolving minerals from the rocks, which unfortunately for UNESCO can be especially damaging in rocks like limestone.

Plus they can cause damage through things like those watery biofilms and root-like hyphae.

And And in some cases, they can even poop out salts, which can be destructive both chemically and physically, if it starts to build up in cracks and force them apart.

Case in point, the Egyptian group applied cladosporium fungi to some fresh stone and found it discolored and weakened.

It had even dissolved some of the stone after just two months.

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To treat those issues, they tried a bunch of different biocides on their stone blocks and found some that worked,

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including synthetic topical antiseptics, as well as natural options like clove oil.

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But we don't want to go indiscriminately killing all life at these UNESCO sites, because in some cases, microbes might actually protect them.

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At Angkor Wat in Cambodia, for example, scientists found that lichens might help protect the stone buildings there from water damage.

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They were effectively shielding the site from the weather, and may also have been pushing out other microbes that could have damaged the site.

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Now, lichens are actually a mix of microscopic bacteria and algae living inside a kind of fungal web, and some of them are microscopic so they might tow the line of microorganism,

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but for the purposes of this video, we are counting them.

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But if you're not team microbe when it comes to lichens, there are still other protective guys under the microscope.

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Some scientists are even experimenting with the idea of purposefully applying certain harmless bacteria

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or amoebas to different archeological sites as a preventative or even restorative treatment.

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In plaques and other microbial communities, including ones from places like murals or ruins, there are protective microbes that may crowd out,

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chemically suppress or directly prey upon the ones that cause damage.

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There are even microbe-targeting viruses we might be able to use.

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One group experimented with using sulfate-eating bacteria to remove unsightly black sulfate-rich gypsum deposits from the base of a famous marble sculpture,

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Michelangelo's Rondonini Pieta.

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The bacteria were mixed into a gel that could be slathered onto the sculpture.

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A day later, scientists came back, washed it off, and found that the deposits were gone.

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So along with all of the publications coming out that highlight microbes' destructive ways, people are experimenting with plenty of them that could help in preservation.

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We often talk about these sites as if they're kind of frozen in time, but in fact, they're constantly changing ecosystems.

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Microbial research helps us understand those changes so we can preserve the sites for generations to come.

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Sometimes if you want a better view of the future, you need to get out a microscope.

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Mot	Prononciation	Sens
microbe nom	/ˈmaɪkɹoʊb/	microbe
bacterium nom	/bækˈtɪəɹ.ɪəm/	bactérie
biocide nom	/ˈbaɪoʊsaɪd/	biocide
biofilm nom		biopellicule
fungus nom	/ˈfʌŋ.ɡəs/	fongus
moisture nom	/ˈmɔɪs.t͡ʃɚ/	humidité
alga nom	/ˈæl.ɡə/	algue
dissolve verbe	/dɪˈzɑlv/	dissoudre
lichen nom	/ˈlaɪ.kən/	lichen
microbial adjectif	/maɪˈkɹəʊ.bi.əl/	microbien
microscope nom	/ˈmaɪ.kɹəˌskoʊp/	microscope
nutrient nom	/ˈnuː.tɹi.ənt/	nutriment
decay nom	/diˈkeɪ/	décrépitude
sculpture nom	/ˈskʌlpt͡ʃɚ/	sculpture
cellulose nom	/ˈsɛljəloʊs/	cellulose

Mot	Prononciation	Sens
break down verbe		tomber en panne
come back verbe		revenir
come out verbe	/ˌkʌm ˈaʊt/	sortir
get out verbe		sortir
make up verbe	/ˌmeɪk ˈʌp/	constituer, composer
open up verbe		ouvrir
take down verbe		décrocher

Structure	Dans la vidéo
Present perfect continu have/has been + -ing — une action commencée avant et toujours en cours	we've been reburying · have been pushing
Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait	is associated · are surrounded · could be crushed
Present perfect have/has + participe passé — une action passée qui compte encore maintenant	has designated · you've entered · have found
Propositions relatives who / which + proposition — une précision sur une personne ou une chose	wood, which can · salts, which can

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