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What’s Ruining Our Ruins?
What’s Ruining Our Ruins?
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Sous-titres (214)
0:00
The United Nations has designated roughly 1,000
0:03
culturally important World Heritage sites around the world.
0:06
But at many of them, something has quietly been going wrong.
0:09
Paintings are flaking away, wood is rotting,
0:12
even stone is slowly dissolving into powder.
0:15
If you’re wondering what’s so powerful that it could take down
0:17
some of our oldest and most protected sites…
0:20
well, this destruction isn’t the product of war or natural disasters
0:23
or other huge events.
0:25
It’s the work of microbes.
0:26
Here’s how some mini microbes are ruining our ruins.
0:29
[♪ INTRO]
0:33
First up, we’re going to the Maijishan Grottoes:
0:35
a series of roughly 200 caves carved into the side
0:38
of a sheer sandstone mountain in the Gansu province of northwest China.
0:43
You have to be feeling brave to cross the soaring walkways that lead inside.
0:48
But once you’ve entered a grotto,
0:49
you can find sculptures and wall paintings from as far back as the 300s.
0:54
But despite standing through 1700 years, the site is in trouble.
0:58
In 2018, experts reported that microbial plaques had started growing on the art!
1:04
As far as we know, it’s not like microbes hate art or something.
1:07
They do this to make a home for themselves or to get nutrients.
1:10
In fact, while a painting might seem like a weird place for life to grow,
1:14
if you’re a microbe, paintings can be full of tasty bits.
1:17
There’s the paint itself, which might contain things like plant oils,
1:21
egg yolk, or animal glue.
1:22
But there may also be layers of organic materials
1:25
like straw or other plant fibers beneath as well,
1:28
which the ancient painters would have slathered
1:31
on the wall to give themselves a smooth surface to work on.
1:34
That is a balanced meal for a microbe!
1:36
As for what kind of microbes, there’s a wide variety of bacteria and algae.
1:41
Both of those organisms can do art-damaging things
1:44
like poop out acids or form gooey biofilms that can trap water.
1:48
You can also get molds and other fungi growing on those ruins,
1:52
which spread their root-like hyphae underneath the surface, looking for nutrients.
1:57
All these little fellas can physically separate the layers of a painting,
2:00
causing bits to flake or fall off.
2:02
They can also cause changes in color,
2:04
either by degrading existing pigments or by adding their own colors into the mix.
2:08
Green algae can turn things, well, green.
2:10
Certain bacteria can do green as well, plus yellow, brown, or black.
2:14
One kind of bacteria can even create a lovely salmon pink.
2:18
But in the case of Maijishan,
2:19
there were mainly white and black splotches appearing on the walls.
2:23
When scientists analyzed the splotches,
2:25
they found that a common decomposing fungus
2:28
was the dominant microbe in the black biofilms.
2:30
Meanwhile, Cladosporium, a super common indoor mold,
2:34
and an unclassified species of fungus were dominant in white biofilms.
2:38
As for what caused the outbreak, they don’t know for sure,
2:40
but it probably had to do with cave critters.
2:43
The decomposing fungus is associated with arthropods, like bugs.
2:47
And fungi can also grow on animal dung or after flooding,
2:50
so animals getting into these caves,
2:52
to shelter from heavy rains, might be contributing.
2:55
In fact, previous work on the splotches also pointed fingers at excess humidity
2:59
as a possible cause and suggested it could be from more human visitors
3:03
or even shifts in the weather thanks to climate change.
3:06
We know this is possible.
3:07
The Lascaux caves in southwestern France contain wall paintings
3:11
from as far back as 22,000 years ago.
3:14
But after their re-discovery in the 1940’s,
3:16
lots of people began visiting, and the carbon dioxide,
3:20
heat, and water vapor from their breath caused microbes to grow.
3:23
The authorities eventually closed the caves to the public and for forty-ish years,
3:27
tried using biocides, including antibiotics, to get rid of those microbes.
3:32
And it worked on some of the microbes.
3:34
But that opened up space for a new fungus to move in,
3:37
which left a whole new set of white stains behind!
3:40
Similar things happened when people tried to disinfect
3:42
the frescoes of St. Paul in Ephesus.
3:45
So biocides don’t always work as well as we hope.
3:48
Another option is manual removal, like using soft brushes, a vacuum,
3:52
and a little bit of elbow grease. …Which they tried in the Maijshan Grottoes,
3:56
along with biocide treatments.
3:58
Those measures seem to have worked well,
4:00
even though this is probably going to be an ongoing project.
4:04
But paintings aren’t the only type of heritage under pressure from microbes.
4:07
We’ve also had some problems with wood.
4:09
But before we go there, it’s time for a quick ad.
4:12
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4:14
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4:19
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5:02
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5:03
In the desert of New Mexico, you can find Chaco Canyon.
5:06
It’s another UNESCO World Heritage site, occupied by the
5:09
Ancestral Puebloan people for about 300 years, starting around the mid-800s.
5:14
While they were there, they built impressive great houses
5:17
and other infrastructure out of stone and wood.
5:19
And so far, it’s stood the test of time.
5:22
But not entirely unscathed.
5:24
For example, in the mid-oughts, experts examined some of the wooden beams
5:27
that made up the buildings and found a significant amount of damage.
5:31
Some was from weathering and other physical processes.
5:34
But some was from microbes.
5:35
Now wood, especially wood in harsh, dry environments like the
5:39
New Mexico desert, can be pretty resistant to microbes like bacteria.
5:43
Wood is tough and durable because plant cells are surrounded by cell walls
5:48
and woody plants in particular pack them especially full of tough,
5:52
hard-to-break-down molecules like cellulose and lignin.
5:55
But wood is vulnerable to fungi, because they have ways
5:59
to get into and even get food from these compounds.
6:02
One of the main trouble makers is a group of fungi that includes brown-rot fungi.
6:06
These little guys specialize in decaying the cellulose in plant cells,
6:10
leaving the colorful lignin behind.
6:12
This turns the wood soft, but leaves the wood’s brown color behind.
6:16
And that’s where they got their name.
6:17
White-rot fungi, meanwhile, turn wood white
6:20
since they decay everything, including lignin.
6:23
Some even specialize in lignin.
6:26
Another major kind of fungal wood decay is soft rot.
6:29
This looks really similar to brown-rot.
6:32
In fact, it’s so similar that you generally need to look at samples
6:35
under a microscope to tell soft-rot and brown-rot apart,
6:38
even though the organisms behind the rot are pretty different.
6:41
And experts have found some brown-rot and a lot of soft-rot setting in at Chaco.
6:46
Some parts of the wood were so degraded they
6:49
could be crushed into a fine powder with even slight pressure.
6:52
Part of the problem may have come from fissures in the wood,
6:55
which can catch moisture and nutrient-rich particles from the environment.
6:59
The perfect conditions for microbes to move in.
7:01
In this case, instead of biocides, we’ve been reburying
7:05
parts of the site since the 1980s.
7:07
The idea is that digging them up likely exposed them
7:10
to the moisture the fungi needed to thrive.
7:13
So reburying them should hopefully remove that moisture and stop further growth.
7:17
As an added layer of protection, conservationists also installed things
7:21
like moisture monitors alongside the buried material,
7:24
as well as waterproof fabric sheets or drains and pipes that can
7:29
funnel surface water away from stuff buried further down.
7:32
Reburial is pretty low-tech, practical, and, compared to trying to replace the
7:37
wooden beams or other materials again and again, a good deal money-wise.
7:41
We like to imagine technology solving all our problems,
7:44
but sometimes the best option for archaeologists
7:46
is to leave things alone and preserve them for the future.
7:49
We can get the technology to fix it later.
7:51
Although eventually everything breaks down, whether it’s paint,
7:54
or wood, or even stone itself, as our last location shows.
7:58
In 2018, scientists took samples from a bunch of sites in Egypt,
8:02
from tombs and obelisks to mosques and even the pyramids at Giza.
8:06
These sites are ancient, and have withstood the test of time.
8:09
But over the years, people have noted damage at some of them,
8:12
including black stains and pitting in the rocks themselves.
8:15
Scientists found two species of a common mold
8:18
along with Cladosporium, one of the fungi found at Maijishan.
8:21
And we’re not just seeing it in Egypt.
8:24
Another desert site, Megiddo, was surveyed in 2023.
8:27
This world heritage site was swabbed from
8:30
the visitor entrance to its major archaeological sites.
8:33
Experts didn’t report damage, but did detect acid-producing microbes.
8:37
As for what a microbe would even want with stone, just like wood or paintings,
8:42
it can give them a home and even food.
8:44
They might even damage the stone itself by doing things like
8:47
dissolving minerals from the rocks, which unfortunately for UNESCO,
8:51
can be especially damaging in rocks like limestone.
8:54
Plus they can cause damage through things like
8:56
those watery biofilms and root-like hyphae.
8:59
And in some cases, they can even poop out salts,
9:02
which can be destructive, both chemically and physically
9:05
if it starts to build up in cracks and force them apart.
9:08
Case and point, the Egyptian group applied Cladosporium fungi
9:12
to some fresh stone and found it discolored and weakened.
9:15
It had even dissolved some of the stone after just two months.
9:19
To treat those issues, they tried a bunch of different biocides
9:21
on their stone blocks and found some that worked,
9:24
including synthetic topical antiseptics, as well as natural options like clove oil.
9:29
But we don’t want to go indiscriminately killing all life at these UNESCO sites.
9:33
Because in some cases, microbes might actually protect them.
9:36
At Angkor Wat in Cambodia, for example, scientists found that
9:39
lichens might help protect the stone buildings there from water damage.
9:43
They were effectively shielding the site from the weather and may
9:46
also have been pushing out other microbes that could have damaged the site.
9:50
Now, lichens actually a mix of microscopic bacteria
9:54
and algae living inside a kind of fungal web.
9:56
And some of them are microscopic.
9:58
So they might toe the line of microorganism,
10:00
but for the purposes of this video we’re counting them.
10:03
But if you’re not Team Microbe when it comes to lichens,
10:06
there are still other protective guys under the microscope.
10:09
Some scientists are even experimenting with the idea of purposefully
10:12
applying certain harmless bacteria or amoebas to different
10:16
archaeological sites as a preventative or even restorative treatment.
10:20
In plaques and other microbial communities,
10:22
including ones from places like murals or ruins,
10:25
there are protective microbes that may crowd out,
10:27
chemically suppress, or directly prey upon the ones that cause damage.
10:32
There are even microbe-targeting viruses we might be able to use.
10:35
One group experimented with using sulphate-eating bacteria to remove
10:38
unsightly black, sulphate-rich gypsum deposits from
10:42
the base of a famous marble sculpture, Michelangelo’s Rondanini Pietà.
10:46
The bacteria were mixed into a gel that could be slathered onto the sculpture.
10:51
A day later, scientists came back, washed it off,
10:53
and found that the deposits were gone!
10:55
So along with all of the publications coming out that highlight microbes’ destructive
10:59
ways, people are experimenting with plenty of them that could help in preservation.
11:03
We often talk about these sites as if they’re kind of frozen in time.
11:07
But, in fact, they’re constantly changing ecosystems.
11:09
Microbial research helps us understand those changes
11:12
so we can preserve the sites for generations to come.
11:15
Sometimes if you want a better view of the future,
11:17
you need to get out a microscope.
11:20
[♪ OUTRO]
