Going Underground

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Original Air Date: 
November 02, 2019

Scientists and explorers have found a whole new world, ripe for discovery, under our feet. The earth's underground is teeming with life, from fungal networks to the deep microbiome miles below the planet's crust. It's an exciting place, and it's changing what we know about the planet and ourselves.


Robert Macfarlane spent a decade exploring caves, mines, catacombs and sewers, on a quest to discover the deep underground. He found a subterranean world of wonder and horror.


Jill Heinerth nearly died when she was trapped by ocean currents inside an Antarctic iceberg. She's one of the world's most accomplished underwater cave divers, often exploring caves no one's ever been in, which show her "the veins of the Earth."

The San Andreas Fault, on the Carrizo Plain.

Do you know what an earthquake sounds like? Geophysicist Ben Holtzman collects recordings from around the world โ€” from the Fukushima disaster to the manmade earthquakes caused by fracking. We hear examples of these seismic rumbles.

cave paintings

Renowned filmmaker Werner Herzog was awe-struck when he saw the Chauvet cave paintings dating back 32,000 years. "You can see clearly that this is the beginning of modern man," he says.

Covalanas panel in the Bernifal Cave.

There's no better way to get a feel for the origins of the human mind than to go and see ancient cave art. Anthropologist Christine Desdemaines-Hugon took Steve and Anne to two French caves with paintings dating back more than 10,000 years.


Show Details ๐Ÿ“ป
November 02, 2019
July 18, 2020
February 27, 2021
October 23, 2021
July 16, 2022
May 27, 2023
Full Transcript ๐Ÿ“„

Anne Strainchamps (00:00):

It's To The Best Of Our Knowledge. I'm Anne Strainchamps. How far underground would you be willing to go?

Robert Macfarlane (00:15):

I knew I wanted to write this book and I wanted to think about this realm and I called up my friend John Beatty. He's a great climber and a great caver. And I said, "John, I need to know if I can do this. I need to know if I can be underground and think about the underground. Take me somewhere and scare the hell out of me."

Anne Strainchamps (00:36):

This is Robert Macfarlane, talking with Steve Paulson, who is just a teensy bit claustrophobic.

Robert Macfarlane (00:45):

So we went for a day's caving down something called Giants Hole. This is like a beginners caving expedition, but it's famous for being very exciting, and there's something called the crab walk in it, this water world rift of limestone that folds like a curtain. And it reaches a point called the vice. As you can imagine, the vice is not a place of great expanse and openness.

Steve Paulson (01:10):

Visions are dancing in my head right now.

Robert Macfarlane (01:17):

Well, imagine you've made yourself very thin and then you've entered into the folds of a curtain and you are now edging sideways within that curtain. And you then reach a point where the curtain narrows even more tightly, that is the vice. And John, who is a little older than me and had drunk a little more beer than me over the years, was unable to proceed through the vice. The vice gripped him, but I was.

Robert Macfarlane (01:45):

I was so thrilled to be down there. I was, later as John put it, like a rat in a drain pipe. It was brilliant and I found myself so excited and I followed that stream on and deeper into the earth. And then at one point the stream itself fell away, and I went on to this space where there was no running water any longer, utter silence, dryness. It was a chamber of storage and tranquility. I came out frightened and thrilled.

Anne Strainchamps (02:31):

The underground, the underworld, is the setting for some of humanity's most primal myths. It's a liminal space where the dead are buried and monsters live. In the old stories, people venture into the underworld at their own peril and return, if they return, transformed. Well, in some ways that's exactly what happened to Robert MacFarlane. The British nature writer spent more than a decade exploring the underground. Caves, mines, shafts inside glaciers, even the catacombs under Paris. What he found is not a dead zone, but a dark world teeming with life from tree roots and fungal networks, to a deep microbiome miles below the crust, all largely unknown and unexplored. Steve Paulson just finished Macfarlane's book, Underland, and asked him to read an excerpt.

Robert Macfarlane (03:43):

We know so little of the worlds beneath our feet. Look up on a cloudless night and you might see the light from a star, thousands of trillions of miles away, or pick out the craters left by asteroid strikes on the moon's face. Look down, and your sight stops at top soil, tarmac, toe. I have rarely felt as far from the human realm as when only 10 yards below it, caught in the shining jaws of a limestone bedding plane first formed on the floor of an ancient sea. The Underland keeps it secrets well. Only in the last 20 years have ecologists succeeded in tracing the fungal networks that lace woodland soil, joining individual trees into intercommunicating forests. In China's Chongqing municipality, a cave network explored in 2013 was found to possess its own weather system.

Robert Macfarlane (04:49):

Why go low? It's a counterintuitive action running against the grain of sense and the gradient of the spirit. Along cultural history of abhorrence exists around underground spaces, associating them with the awful darkness inside the world, in Cormac McCarthy's phrase. Fear and disgust are the usual responses to such environments; dirt, mortality and brutal labor the dominant connotations. Claustrophobia is surely the sharpest of all common phobias. I've often noticed how claustrophobia, much more so than vertigo, retains its disturbing power even when being experienced indirectly as narrated. Hearing stories of confinement below ground people shift uneasily, step away, look to the light as if words alone could wall them in.

Steve Paulson (05:55):

Okay. You've taken us down there and that's great. Rob, your first book was about mountains and your personal history as an avid climber and the thing about mountains is that for all of their danger, they are places of incredible beauty. I mean, it's almost the definition of awe inspiring landscapes. And I guess I'm wondering if that's also true of the places below. Are these also places of beauty, maybe even of awe?

Robert Macfarlane (06:24):

They are certainly places of awe, they're also places of imprisonment, incarceration, concealment, disposal. They're the place we've put the things we fear most and disgust us most. So it's a harder place down there, there's no doubt.

Steve Paulson (06:42):

So you went on various journeys underground, into caves, mine shafts, the catacombs of Paris. What did you find most surprising about any of these trips?

Robert Macfarlane (06:55):

How lively the world is in its material forms, might be one answer to that. How loving my return to the upper world was, might be a second answer to that.

Steve Paulson (07:08):

Thank God I'm out of here, I can see the sun again.

Robert Macfarlane (07:10):

Yeah. I can see the sun again. I mean, it's no coincidence that in the Tibetan tradition of the bardo, the pilgrimage that is also a rebirth, there is often a passage through a confined cave space in the imaginative version of that journey, to come up to the surface again from darkness. These are dark places, but they're also places of visions.

Steve Paulson (07:30):

You call this the Underland but there's definitely the sense that you were descending into the underworld with all the mythic weight that goes along with that. I mean, this is where Hades rules, where the dead are buried, where the living might visit but will be lucky to come out alive. Did you feel the presence of death, whether metaphorical or actual, when you were underground?

Robert Macfarlane (07:53):

I did, I did. And I think this isn't a book I could have written before my 40s, by that time in anyone's life you've known death a few times and yes, the oldest stories we have really, the Epic of Gilgamesh, 2,100 BC in Sumeria, is about someone going to the underworld to bring back news of the dead children of Gilgamesh as well as to look for a precious thing.

Steve Paulson (08:20):

This is fascinating. So it's this long tradition of going to the underworld to seek knowledge?

Robert Macfarlane (08:26):

Exactly, exactly. And we are still doing that. We have glaciologists now who are boring, augering down into the ice record, up to a mile down to bring back knowledge of past climates, to foretell our future climates from that knowledge. This is a place to which we have gone, even though it contains darkness which seems the opposite of knowledge, to seek knowledge.

Steve Paulson (08:51):

So we've been talking about the underground as if it's a dead zone but biologically, isn't the underland actually thriving with life? In fact, you point out that scientists say that there are some places where there is just an incredible amount of biodiversity underneath the earth crust.

Robert Macfarlane (09:07):

Yes. Oh my goodness. We are only just beginning to fathom the incredible diversities and depths of life in the crust in the earth. The rhizosphere, the soil, if we just take that top level, is a fabulous, vital substance and layer that we hardly comprehend. Early this year, scientists revealed that they had found that the deep microbiome, up to 20 kilometers down into the crust, there is life. And this life is of such volume that it exceeds by hundreds of times, the total biomass of all human life on earth right now. It's so diverse, they call it the Amazon or the Galapagos of the underworld. This is all-

Steve Paulson (09:49):

Wait, what kinds of organisms are living there?

Robert Macfarlane (09:51):

It's all microbial life. It's bacteria predominantly, but in such number and with such complexity that scientists are reeling back at this, I think they call it biological dark matter, which is a great phrase. And then there is this fungal network, the mycorrhizal network, known durably, wittily, brilliantly as the wood wide web which-

Steve Paulson (10:15):

The wood wide web. That's good.

Robert Macfarlane (10:17):

Have you heard that one before?

Steve Paulson (10:19):

Not before reading your book.

Robert Macfarlane (10:21):

I wish it were mine. Of course it's been around for 20 years or so now, but yeah, these are the hidden buried fungal, the mutualism between fungi and trees that forms a network.

Steve Paulson (10:33):

These are the fungal networks that extend out from the roots of trees that actually allow trees to communicate with each other.

Robert Macfarlane (10:40):

Yes. So the popular description is, this is the social network of trees. We have to be careful how we describe this, but they can pass resources between one another and they can pass, to some degree, signals between one another.

Robert Macfarlane (10:52):

Wow. All of that is happening, buzzing away, and suddenly it shakes the ground you walk on.

Steve Paulson (10:59):


Steve Paulson (11:00):

So we've been talking mostly about natural places underground, but you also went down underneath the city of Paris into the catacombs down there, and you say that there's basically a huge invisible city that's like the mirror image of what is above ground.

Robert Macfarlane (11:17):


Robert Macfarlane (11:18):

Wow. I mean, some of your listeners who've been to Paris, I think, that would have been into the small faction of the catacomb, labyrinth or network that is available for tourists, but it's a tiny portion of the hundreds of miles of network that do exist under predominantly Southern Paris. So more than any other city, apart from maybe Odessa, there is this sense that, as in a kind of Borges story or Calvino story, the city has its invisible city.

Steve Paulson (11:46):

So how much of this can you actually walk through? If walk is even the right word.

Robert Macfarlane (11:53):

Walk, swim, wade, crawl, scream. I suppose this depends how you get there, and I got there by, shall we say, known formal means.

Steve Paulson (12:04):

This is not exactly above board to go exploring in the catacombs under Paris.

Robert Macfarlane (12:09):

No, it's neither above ground nor above board. But this is urban exploration which is one of the names that goes by, but their lovely French names for the people who love going down into the catacombs are called cataphiles or cataphilles. And the police who specialize in policing this subculture are called cataflics. And if you take music down there, you play it on your cataboom box and so on and so forth.

Steve Paulson (12:33):

So there's a whole culture down there of people who hang out in these areas?

Robert Macfarlane (12:37):

Yeah. And the quarry men, through the centuries, cut rooms for themselves, the network is predominantly made up of tunnels which were cut to a standard width and height predominantly, and that's where the stone was brought from, but the quarry men also cut rooms for themselves. They tend to be low, but these become parties zones. So I came through one of the most frightening, fearful, claustrophobic experiences of my life and emerged into a room where three strangers were pressing glasses of vodka into my hand and playing the jams going underground on a cataboom box. This was like a postmodern Tolkien down there.

Steve Paulson (13:15):

Not exactly where Gimli was hanging out.

Robert Macfarlane (13:17):

Well, Gimli would not have banged his head.

Steve Paulson (13:20):

Yeah, yeah. So speaking of claustrophobia, there's a passage that gets at how just incredibly, oh my God, confining, this must have been for you. Could you read this?

Robert Macfarlane (13:32):

Yeah, I will, I will gladly do that. The approach to the Salle du Drapeau, the room of the flag, is the only time I feel real fear in the Parisian catacombs. It's early evening in the upper city by the time we get close to the room down in the invisible city. We are heading northwest along a tunnel with no side turnings, the ceiling of which is dropping steadily lower. I walk with bent neck and with hunched shoulders, then I have to lean at the waist and then it last I have to drop to my knees and can only crawl forwards. Ahead of me past Lina, the tunnel seems to cinch to a dead end. I wait for Lina to admit that she's at last led us the wrong way. Lina says nothing. The yellow of the limestone ahead glows in her torch light. She shrugs off her pack, pushes it behind her, loops one of its straps around one of her ankles and then eases herself headfirst into what I can now see is a tiny floor level opening, perhaps 18 inches high where I thought the tunnel ended.

Robert Macfarlane (14:36):

My heart shivers fast, my mouth dries up instantly. My body does not want to enter that opening. "You'll need to pull your pack along with your toes here," says Lina. Her voice is muffled. "And from now on don't shout or touch the ceiling." Fear slithers up my spine, spills greasy down my throat, nothing for it, but to follow. I lie flat, loop pack to foot, edge in head first. The clearance above is so tight that I, again, have to turn my skull sideways to proceed. The clearance to the sides is so scant that my arms are nearly locked to my body. The stone of the ceiling is cracked into blocks and sags around the cracks. Claustrophobia grips me like a full body vice pressing in on chest and lungs, squeezing breath hard, setting black stars exploding in my head.

Steve Paulson (15:28):

Okay. That just sounds awful, awful.

Robert Macfarlane (15:32):

It was awful.

Steve Paulson (15:33):

Why would you want to do this? I get it, you're writing the book and you'll have to go and describe the places you're writing, but really, you really want to go there?

Robert Macfarlane (15:43):

No, I did not want to go there. As I say, my body does not want to enter that opening. So the upper city part of me is screaming. "No way. Get out of there buddy, reverse, say no." But we had to get to the Salle du Drapeau and that was that. But then what happens is we're further in and wriggling along dragging the pack. The rock above me starts to vibrate and then the rock below me starts to vibrate and I realized that we are under a Metro Line and that there is a train coming overhead, and that the vibrations from the train are passing through the rock and then through my body as the transmitting medium and then into the rock beneath me. And something about that was so extraordinary and so appalling that I'm glad now, sitting on the fourth floor of a building, that I was there.

Steve Paulson (16:34):

Wow. I have to tell you, as I was reading your book, there were a few passages, this was one - and there was an earlier one where you're in a cave and there was some horrible accident decades ago, where someone was buried alive. And I was reading late at night and I get claustrophobic and if I do I have a lot of trouble sleeping. I just had to stop, I had to put your book down. I mean, I was sweating and it was just like, man, I was just reading it but I did not want to go there.

Robert Macfarlane (17:00):

I am thrilled to hear that. It seems to me the only situation in which a writer is glad to hear that a reader had to put the book down.

Anne Strainchamps (17:16):

That's Robert MacFarlane, author of Underland, a deep time journey. And by the way, Steve did a longer interview with him, which you can read in Nautilus Magazine or on our website at ttbook.org. So it's one thing to go crawling through caves. Now imagine doing it under water. It's obviously not for the claustrophobic or Steve Paulson, but if you have nerves of steel, insatiable curiosity and really love deep water, you could be a cave diver.

Jill Heinerth (18:20):

So I jumped in with my diving partners, Paul and Wes, and we descended down into the iceberg to shoot some footage for this film called Ice Island.

Anne Strainchamps (18:32):

This is Jill Heinerth diving inside an Antarctic iceberg.

Jill Heinerth (18:41):

We got down to the sea floor and we were filming these different filter feeding organisms. And we swim in into the iceberg and we kept going and going and going. And then I felt the current getting a little bit stronger and stronger. And the other thing I felt was that I had a pin hole in the glove of my dry suit. My hand was getting wet with water that was 28 degrees Fahrenheit, which is incredibly painful. So, as the current was getting stronger and my hand was getting more and more painful, I turned to the guys and I called the dive. I gave him a thumbs up signal that means let's turn around. And when we turned around, the current was accelerating so strong that we were having difficulty swimming against it. Within a matter of minutes, we couldn't swim against it. We were driving our hands into the sea floor trying to pull our way forward and my biceps were just quivering, trying to move in a positive direction. We couldn't get out.

Anne Strainchamps (20:07):

We'll find out what happened after this. I'm Anne Strainchamps, it's To The Best Of Our Knowledge from Wisconsin Public Radio and PRX.

Anne Strainchamps (20:26):

Okay, we left Jill Heinerth, one of the world's foremost cave divers, trapped inside an iceberg. And not just any iceberg, the largest moving object on the planet, an iceberg the size of Connecticut. When it calved away from the Ross Ice Shelf, Jill and her team convinced National Geographic they could do something nobody had ever done before, Swim inside an iceberg's underwater tunnels and crevasses and capture it on film. The expedition was dangerous, maybe impossible. So what happened?

Jill Heinerth (21:01):

We slowly worked our way towards the entrance and Wes was yelling, "Help me with the camera." And I was thinking, "Screw the camera, we're going to die." I really thought we weren't getting out. When we finally got to the vertical shaft that led back towards the surface, the current and the fresh water melting from the iceberg were descending in a vertical down current, literally pinning us down. But I had recognized these little fish, these white transparent ice fish that were living in the walls of the ice. So when I got to that ice wall and I couldn't grab it in any other way, I started evicting ice fish with my fingers and using these as handholds to climb the wall and get out of the current, back to safety.

Anne Strainchamps (21:57):

Wow. There were people waiting for you, right? They must have been frantic.

Jill Heinerth (22:02):

Oh, they were absolutely concerned. I mean the three people, the only people who were cave divers with advanced life support were already in the cave, so there would be no rescue and we were two hours late.

Anne Strainchamps (22:16):

God. Had anybody ever explored inside an iceberg before?

Jill Heinerth (22:21):

No, no. It was a first, and when we pitched the project, I'll be honest, it was a hypothesis. I mean, we didn't know what we would find when we got there. I mean, that's what exploration is. If there was a handbook we wouldn't be explorers.

Anne Strainchamps (22:35):

I have to confess before I read your book, it actually hadn't really occurred to me that there would be caves underwater. I don't know why not, but I'm probably not the only person. So can you-

Jill Heinerth (22:49):

No, it's pretty abstract.

Anne Strainchamps (22:51):

So tell me about underwater caves.

Jill Heinerth (22:54):


Anne Strainchamps (22:54):

Are there lots?

Jill Heinerth (22:56):

Yeah. I mean the earth is like a sponge really, I'm swimming within the pores of that sponge. Sometimes I get into a cave well inland, way, far away from the ocean. But at other times I dive into a small hole in the sea floor that enables me to travel through these vast conduits, these tunnels full of water inside the planet.

Anne Strainchamps (23:19):

How far do they go?

Jill Heinerth (23:21):

Well, the longest caves are generally agreed to be in the Yucatan Peninsula, in the Riviera Maya. And I started exploring those back in the mid 1990s and we were slowly linking one cave to the next cave to the next. And we agree that it's probably one giant cave there, many, many hundreds of miles of passages. The deepest caves in the world, again, are still being explored. But many of them are over two kilometers deep now.

Anne Strainchamps (23:56):

That must, I don't know, change the way we think about the planet somehow.

Jill Heinerth (24:01):

Well, it does to me. When I'm cave diving inside a water-filled space, I feel like I'm swimming in the veins of mother earth. I'm in the sustenance of the planet, that very drinking water that we draw up from the ground and use to supply humanity and agriculture and industry. It's like I'm in the very works of the planet.

Anne Strainchamps (24:26):

How did this get started for you? Was there a gateway cave dive, the one that got you hooked?

Jill Heinerth (24:31):

Well, when I first learned to dive, I just became a certified scuba diver on the fourth dive of my class. I went into a place called The Grotto in Tobermory, Canada. It's a little swim-through tunnel that then allows you to rise up inside a cave that actually breaks the surface of the water. That was probably a bit of a stretch for a certification dive. But when I swam through that tunnel and was moving in this three-dimensional space, just by inhaling to move up or exhaling to drop down, it just felt magic to me.

Anne Strainchamps (25:09):

It sounds like birth.

Jill Heinerth (25:12):

Kind of, yeah. I guess it's the womb of mother earth, yeah.

Anne Strainchamps (25:17):

Yeah. Something primal. So for a long time, it wasn't humanly possible to explore the kind of caves you've explored, that's much more dangerous than an ordinary scuba diving and much more technical. Can you give me an example of a time when something went wrong?

Jill Heinerth (25:35):

Well, I had a dive that was over 300 feet deep vertically, and then well into a cave that had what we call a series of restrictions. A restriction is where you're literally squeezing your body through a space it doesn't want to fit through, to get to the next big room. And at 300 feet of depth, all of a sudden I heard this loud explosion. It sounded like someone was taking a scuba tank and smashing it against the wall of the cave. And simultaneously my rebreathers started to malfunction and spew pure oxygen into my breathing loop, and that could have been immediately lethal because too much oxygen to a diver at depth can cause seizures and then drowning. So I had to immediately shut down the machine and move into a manual operation to get myself back safely. And it turned out that a lithium battery had literally exploded in the life support pack and blew a hole in the back of the rebreather. So I had to get back without any of the electronics.

Anne Strainchamps (26:44):

Oh my God. I know you know what the next question is going to be. Why would you want to do something that's dangerous and then go back and do it over and over again?

Jill Heinerth (26:54):

People are really surprised, but I think of myself as risk averse.

Anne Strainchamps (26:58):

You're kidding.

Jill Heinerth (27:01):

I mean, when someone gives me a challenge to do something that nobody's done before or go someplace nobody's ever been before, it's just that. It's a challenge and a problem solving exercise where I try to bring the right people, the right equipment, the right training together so that I know that I can survive those worst case scenarios. People that do it for a long time, the lifers, they're a lot more like me. They're more risk averse.

Anne Strainchamps (27:28):

That's why they're still alive.

Jill Heinerth (27:30):

Oh yeah. Yeah. I mean, it's really, really dangerous and I have a list of more than a hundred friends that have died cave- and technical diving.

Anne Strainchamps (27:40):

A hundred.

Jill Heinerth (27:41):

Yeah. It's a lot.

Anne Strainchamps (27:44):

How do you carry that much grief?

Jill Heinerth (27:48):

It's hard. I mean, there are some people within my sphere of friends that I almost look at as marked for death. Like I know I won't be surprised when I get the phone call, but then there are others that just shock me to my core and I grieve all of them equally.

Anne Strainchamps (28:08):

Do the ones you feel like are marked, do they know you feel that way?

Jill Heinerth (28:13):

Oh yeah. Yeah. I've had some pretty sobering conversations with friends about what worries me.

Anne Strainchamps (28:23):

How do you even have that conversation?

Jill Heinerth (28:26):

Oh man. I remember one where we were on the back deck of my home. I was having a barbecue for friends and six of us were trying to convince a friend not to do a dive he had planned for the next day. And he kept saying, "Oh, you don't know, I'm going to make my mark, this is my opportunity." And we tried really hard the whole evening to convince him not to do it and he died that next day.

Anne Strainchamps (28:57):

Oh my God.

Jill Heinerth (28:58):


Anne Strainchamps (28:59):

What happened? Where was he diving?

Jill Heinerth (29:02):

Oh, it was a cave in Florida called Ginnie Springs, Devil's Ear cave system. His dive involved taking off his rebreather life support, switching to another type of gear and squeezing through a small restriction and going further. But when he returned and his rebreather was flooded, he had a series of bottles dropped like bread crumbs on a trail to lead him back to the entrance in case something went wrong. But it wasn't quite enough, and he died literally within arms reach of the next gas supply. It was just tragic.

Anne Strainchamps (29:38):

And when cave divers dive that far underground, how does anybody find them?

Jill Heinerth (29:46):

Well that's the thing. It's something that we take care of within our own community. So we have almost like a phone tree of cave divers with training and in recovery. And when somebody is lost and hasn't come home, we gather the right people together, fly to wherever that is and eventually recover the body.

Anne Strainchamps (30:09):

Have you done that?

Jill Heinerth (30:10):

Oh yeah. Yeah. When you're underwater searching, you think, "Oh God, I hope we find him soon, but I hope I'm not the one." It's extremely, emotionally difficult.

Anne Strainchamps (30:25):

We've been talking about the dangerous side, the perilous side of cave diving. But what does it feel like to be far underground in a place that nobody has ever been before? And there's a good chance that nobody else will ever be there again.

Jill Heinerth (30:43):

It's akin to walking on the surface of the moon. To me it's beautiful, and having a chance to document these places and capture the science, capture the film, the video and bring it back is incredible. But the focus is just laser sharp. You're never so present and in the moment. There's nothing clouding your mind, except just absorbing the opportunity in the spectacle.

Anne Strainchamps (31:13):

Is there a science that comes out of trips like this, besides the thrill, besides the, "Okay, we're exploring it for the first time." Why does it matter?

Jill Heinerth (31:24):

Oh, there's so much. The biology of underwater caves teaches us about evolution and survival. Mapping underwater caves all over the planet helps us understand the hydrology, the plumbing of the planet and connects us to the very idea that everything we do on the surface of the earth is going to be returned to us to drink. I'm like the canary in the coal mine that gets to communicate about the things that I see. I mean, we also get to work with archeologists and paleontologists uncovering the remains of previous civilizations and ancient animals.

Anne Strainchamps (31:59):

Really? You found ancient civilizations under the water?

Jill Heinerth (32:03):

Oh yeah. I work with archeologists, and we found the remains of Mayan sacrifices, we found burial niches with people and pottery and artifacts in them. We found Ice Age bears in Mexico and extinct sloths in Cuba. There's so much inside of caves, they are absolute museums of natural history.

Anne Strainchamps (32:37):

That's Jill Heinerth. Her memoir is called Into the Planet: My Life as a Cave Diver. We'll travel from sea caves to the fault lines beneath the earth next, and hear what an earthquake sounds like. I'm Anne Strainchamps, it's To The Best Of Our Knowledge from Wisconsin Public Radio and PRX.

Anne Strainchamps (33:12):

This is a sound you should pray you never hear in person. That's the sound of an earthquake, not just any earthquake. You're listening to the Tohoku, Japanese earthquake on March 11th, 2011. There was a magnitude 9.1, one of the largest ever recorded, the tsunami that followed caused the nuclear disaster at Fukushima. This sound, recorded at the surface near the epicenter, is condensed from two hours of audio.

Anne Strainchamps (33:49):

Geophysicist Ben Holtzman has been collecting and recording sonic signatures of earthquakes like these for years. He's the founder of the SeismoDome, the earthquake simulator at the American Museum of Natural History in New York and Charles Monroe-Kane, who loves big sounds, wanted to know how you can actually listen to an earthquake.

Ben Holtzman (34:17):

If you're very close to where the earthquake source was and the crack that ruptures the surface and you see a displacement of the ground, there'll be enough high-frequency energy to actually hear, that's transmitted into the air.

Charles Monroe-Kane (34:35):

So it sounds like though you wouldn't want to be in that space where it actually-

Ben Holtzman (34:40):

You don't want to be anywhere near that, no.

Charles Monroe-Kane (34:50):

So how do you then record these sounds?

Ben Holtzman (34:54):

We're taking data from seismometers, which are like very, very sensitive microphones that are attached to the ground or even holed in the ground. But they're taking vibrations of the ground and converting those into electrical signals.

Charles Monroe-Kane (35:14):

We have a lot of recordings we're going to talk about, but one of them I found so fascinating is you have this one recording of earthquakes that sent sound waves all the way across the earth and then back again. I'm not even sure how to wrap my head around that. So what are we listening to right now?

Ben Holtzman (35:31):

It's a lot like when you throw a pebble into a pond and you see the waves propagate away from where the pebble hit, except that in this case the pond is a sphere. So they'll emanate out from the source and then focus on the other side of the planet and then keep going. So any earthquake bigger than a magnitude four and a half or so, will send waves that go all the way around the planet.

Charles Monroe-Kane (35:59):

And then what we're listening to right now is from the Sumatra earthquake. Can you tell me a little bit more about that earthquake so we understand what we're listening to.

Ben Holtzman (36:07):

Yeah. So, that is one of the biggest earthquakes ever recorded. You can think of that crack that ruptured this boundary between two plates, and that crack was about the length of California. And it propagated, so the tip of the crack moved about the length of California in about 13 seconds and sent that seismic energy around the planet. It was so large that that energy... the planet kept vibrating for about three months or so.

Charles Monroe-Kane (36:47):

Wow. Does that have a physical effect? I mean, do we feel it?

Ben Holtzman (36:55):

Yeah. We wouldn't feel it directly. So in New York, the ground went up and down about a centimeter, but it happened too slowly for us to feel. So it went up and down in maybe a hundred seconds on that order.

Charles Monroe-Kane (37:15):

I have this friend, she's a pretty close friend who lives in Berkeley, born and raised there. And she said she still never gets used to earthquakes. They're very disconcerting for her. When you come to the sea, you expect to sea to be a tempest, to be dangerous. But the ground, I think, we all see the ground as solid, you grow up on solid ground, it's meant to be solid. She said when the earth moves, she feels like she's betrayed by the natural world. The earth isn't solid, is it?

Ben Holtzman (37:41):

The earth is basically a liquid with a crust on it. The mantle is always convecting. So in millions of year timescales, the interior is basically like a preboil. It's overturning, it's churning, driven by the heat coming out and that's what's driving the plates and then the plates, where the earthquakes are, are this very, very thin layer that's just cold enough so that there's elastic energy that builds up across faults where they're stuck. And then they're stuck and stuck and stuck until the energy passes through some threshold and then gets released suddenly as an earthquake. So you can think of it as a big soup with a crust on top.

Charles Monroe-Kane (38:27):

Man, that doesn't make me feel like I'm on solid ground at all.

Ben Holtzman (38:31):

You're not, yeah.

Charles Monroe-Kane (38:32):

You're not, okay, let's keep that in mind.

Ben Holtzman (38:34):

Change your reference frame and you'll be fine.

Charles Monroe-Kane (38:37):

All right. Thank you very much.

Ben Holtzman (38:38):

Tell your friend.

Charles Monroe-Kane (38:40):

Hey, I'll call her and I'm sure she'll feel really better after this.

Ben Holtzman (38:43):


Charles Monroe-Kane (38:51):

Not only do you have these sounds that you get from the earthquakes, you also have this amazing collection of accidental recordings by people who happen to be recording when an earthquake happens. Take us to Friuli, Italy in 1976.

Ben Holtzman (39:04):

Yeah. So there was this teenager transferring a vinyl record of Pink Floyd's Wish You Were Here, the P wave arrives. So these are what dogs pick up. You hear a scratch and that's the S wave arriving and then the rumble, and then you hear people starting to yell.

Charles Monroe-Kane (39:41):

It takes about 20 seconds for the P wave to hit before you hear the human reaction, either a child crying for the mother, the chaos. So is that how long it takes? Is there a 20 second lag that we have before we know an earthquake starts from studying these waves? That doesn't seem like very much time to know it.

Ben Holtzman (40:01):

Here's an illustration of how we can use that. So in Japan, they have by far the highest density of seismometers over the largest area on earth, and they use it to send out earthquake early warning across the country, so they can tell immediately roughly how big and where an earthquake is. They can stop a bullet train or slow a bullet train down through the whole train network across the country the moment that they register an earthquake that's above some threshold.

Charles Monroe-Kane (40:47):

In 20 seconds?

Ben Holtzman (40:49):


Charles Monroe-Kane (40:50):


Ben Holtzman (40:51):

Yeah, yeah. 20 seconds is enough time to send off an alarm to hopefully get people out of their houses or buildings or under a table and to slow trains down.

Charles Monroe-Kane (41:04):

There's a modern sound of fairly recent earthquakes that, to me, were the scariest. You're from Oklahoma. Can you tell me why we're having earthquakes in Oklahoma and how you study those?

Ben Holtzman (41:26):

Yes, yes I can. A few states allow injection of wastewater from fracking for natural gas extraction. One of those states is Oklahoma, that allows those fluids to be stored underground. And so they're taking those fluids and injecting them into rock formations that used to have oil in them that they took out years ago. So there are a lot of holes in those reservoirs, and they're injecting that fluid at high pressure, very high pressure because they want it to go deep into that reservoir and stay there. So because it's a high pressure, it has been effecting old faults. And so these faults get pried open and triggered and stresses that people didn't really know were they're get released. So Oklahoma now has more earthquakes than California.

Charles Monroe-Kane (42:41):

Oh, Jesus. That's incredible.

Ben Holtzman (42:44):

Yeah, yeah. It really is.

Anne Strainchamps (42:52):

Ben Holtzman is a geophysicist and founder of the earthquake simulator at the American Museum of Natural History in New York, the SeismoDome. This hour is all about the mysterious and largely unexplored world beneath the Earth's surface. Today, scientists and explorers are inventing all kinds of new technology to go deeper, further underground. But tens of thousands of years ago, our human ancestors did the same thing, and we know because of the mysterious haunting paintings they left behind. There are some privately owned caves in Southwest France that you can visit. A few years ago, Steve and I and our family were lucky enough to spend a couple of days exploring two of these caves, along with an expert on prehistoric cave art, the British born anthropologist, Christine Desdemaines-Hugon. Steve has the story.

Steve Paulson (43:58):

This has been a lifelong dream of mine, to visit one of these old French caves. I couldn't imagine what it would be like. There's art that was made more than 10,000 years ago. So we ended up by the side of the road, there was a beautiful field an old stone barn. A few minutes later, Gilbert Pemendrant, he's the owner of the cave we were visiting there in the fall, gets out of his car and then we walk up a hill through this lovely forest, and then it's like something right out of a fairy tale. There's a door set into the side of a hill.

Christine Desdemaines-Hugon (44:31):

All right. So we've just walked through a beautiful horn beamed forest to get to the entrance, and there it is up on the hill, and I can't imagine a more amazing cave entrance. It's almost as if you're about to discover it for the first time yourselves.

Steve Paulson (44:45):

It's a really hot summer day, but inside the cave it's cold. It's about 50 degrees.

Christine Desdemaines-Hugon (44:50):

[foreign language], everybody put their sweaters on.

Steve Paulson (44:52):

It's cold, it's dark, it's damp, it would be hard to keep a fire going. Basically it would be very unpleasant to live there, which raises the question. Why did people make art there? What was it for?

Christine Desdemaines-Hugon (45:03):

I have no idea. Caves are very special places. When you enter a cave on your own, you will see that it has very strong impact on you physically. It's like entering a church that has an impact on your mind and on your imagination. And the same way a cave is perhaps even more extraordinary because there's something to my mind, wonderfully organic about caves.

Steve Paulson (45:23):

And also something timeless because you don't know if it's night or day.

Christine Desdemaines-Hugon (45:29):

And it's magical. There is something magical about the underworld.

Christine Desdemaines-Hugon (45:33):

So here we are in the heart of the cave, the deepest part and we're going to see some very mysterious things.

Steve Paulson (45:40):

The first thing we see are these two hands.

Christine Desdemaines-Hugon (45:44):

Did you see the shape of the hand? You see the fingers and the thumb and here's another one, the thumb and the forefingers. These are the only two engraved hand prints that we know of in prehistoric art. These are the only ones that have actually been engraved. So that's quite exceptional in itself.

Steve Paulson (46:02):

One of the things about being in a cave like this is, you forget that this was all made more than 10,000 years ago. I mean, it's as if it was made yesterday. These hands could be from someone today and so you have the sense that you are reaching across time and then Christine points out something even more remarkable.

Christine Desdemaines-Hugon (46:22):

The most amazing figure here is the face. It's the only realistic face that I know of in prehistoric art. You've actually got the eyes and the eyebrows and two nostrils, the mouth. So you have a face looking at-

Steve Paulson (46:39):

And straight at us, that's why it's so amazing.

Christine Desdemaines-Hugon (46:42):

... straight at us, through the calcite, searchingly almost, meeting our eyes. I mean, that is something that I find extraordinarily moving myself. We're going to continue.

Steve Paulson (46:57):

But not all the caves in France are the same. So Bernifal is a tiny little cave and by contrast, Rouffignac, another cave we visit, is a big cave with caverns that extend for miles and there's a group of French school kids that are there, and we hop on to a little electric train and we go deep under the ground into the cave.

Christine Desdemaines-Hugon (47:20):

We are now one kilometer from the entrance. People came this far holding their tools, crayons, chisels, look at this beautiful horse for instance, the details drawn by the artist lying on his or her back, very friendly and happy animals as you can see. It's why I always call this a happy cave, a joyful cave, a joyful experience, but you can also see a very large mammoth in the center. And we also have ibex mountain goats upside down that one. Here's another big bison.

Steve Paulson (47:58):

This cave is teeming with life. There are animals everywhere, all over the walls, all over the ceilings. There's a woolly mammoth with shaggy fur, long tusks. Rhinoceros bears, ibex, and they overlap each other. Sometimes they're on top of each other. Sometimes there's a procession of animals and they are drawn with crayons made out of minerals. So they are different colors, red and black, ochre and white.

Christine Desdemaines-Hugon (48:22):

The modern aspect of the work is what fascinates me. They were already exploring all the top lay effects of perspective. Three-dimension, abstraction, cubism, all this exist in paleolithic. Picasso said, when he saw the art, that he'd met his masters, and that nothing he could do hadn't already been explored by Cro-Magnon artists.

Steve Paulson (48:48):

But then Christine points out something that none of us had seen.

Christine Desdemaines-Hugon (48:49):

Six horses, three on the right, three on the left. And in the center, something that nobody sees it all, is a very frankly drawn horse's head and neck. So centrally placed. It evidently was probably the most important figure of the ceiling. And this is where you become face-to-face with a mystical impression that perhaps the most sacred and the most spiritual and the most mystical is what's the least visible. See how complex this all becomes. So I'm going to ask him to switch off the light and let's be quiet.

Steve Paulson (49:22):

At Bernifal, the very last thing we do is we stand in darkness. Gilbert, our French guide, has turned off his lantern. Christine has turned off her flashlight, it is totally dark. We can hear the water dripping. I don't know if I want to say I felt the presence of the spirits there, but it almost felt like that. And then Gilbert the guide, we suddenly hear him walking away and he has left us.

Anne Strainchamps (50:03):

Anthropologist Christine Desdemaines-Hugon and my family in one of the prehistoric caves in Southwest France. Her book about the cave paintings of the Dordogne is called Stepping Stones. And that's it for our show today, but there is always more on our website at ttbook.org, where you can sign up for our newsletter and subscribe to the podcast. To The Best Of Our Knowledge is produced at Wisconsin Public Radio by Charles Monroe-Kane, Mark Riechers, Shannon Henry Kleiber and Angelo Bautista. Our sound designer and technical director is Joe Hardtke, our executive producer is Steve Paulson, and I'm Anne Strainchamps. Thanks for listening.

Speaker 7 (50:46):


Last modified: 
May 26, 2023