“This seems like something that should be being discussed on the floor of the US Senate right now, like, what are we going to do when this happens? You want to talk about being oblivious to the ground at your feet? This is ground that we are just completely oblivious to, and it has the potential to wreak havoc on the planet.”

Life depends on a thin layer of soil, wrapped around the planet like the skin of an apple. A quarter of all life itself actually lives in soil. We grow our food in it; it is a source of medicines and illness; it filters our water; it provides nutrition for our food. Its importance is incalculable—but it’s easy to miss.

From his porch in Los Angeles during wildfire season, Dan Crane explores how local stories of mud and dirt can be part of the global story of life itself.

Presented by Dan Crane
Written by Ian Steadman
Sound design by 
Laura Irving

Made with the support of The Bill & Melinda Gates Foundation

Featured guests

Music & audio credits

Show notes

Some additional information and resources not directly linked to within the transcript (below):

  • Some footage of Dan in action as his alter-ego “Bjorn Turoque” from the 2005 Air Guitar Championships (knocking out a rendition of “Set Me Free” by Sweet).
  • Information and images/video of the devastation cause by the 2017 wildfire season in northern and southern California.
  • NPR explains why Smokey the Bear has made wildfires worse—it’s part of an excellent five-part series on forest fires you should really check out.
  • Some satellite imagery of Siberian forest fires happening while this episode was in production (and still happened as it airs).
  • An in-depth feature explaining just how dust from the Bodélé Depression in Chad sustains and fertilizes the vegetation growing in the Amazonian basin.
  • Plus, a visualization of the trans-Atlantic dust flight from NASA:




DAN CRANE: Late last year my city caught fire.

PBS CLIPNew evacuations are spreading across the south California coast tonight as wildfires burn out of control. The flames so far have destroyed over 200 homes and other buildings, forcing tens of thousands of people to leave.

DAN CRANE: And because it’s LA, the headlines focused on the celebrities.

ENTERTAINMENT TONIGHTHollywood on the run from multiple wildfires raging in southern California.

ENTERTAINMENT TONIGHTThis morning, actress Leah Michele was evacuated from her Brentwood home. She posted this video from her car, before hitting the red carpet at an event at the Hollywood Reporter.

ENTERTAINMENT TONIGHTEllen DeGeneres and wife Portia de Rossi forced to evacuate California home due to wildfires.

ENTERTAINMENT TONIGHTActor Rob Lowe posted this dramatic video of his commute home, and told his fans: we are safe, others aren’t, pray for them.

DAN CRANE: Here’s the thing. I technically qualify as one of those celebrities. Just… not the famous kind. As Conan O’Brien would say…

CONAN O’BRIEN: My next guest iswidely considered the second-best air guitarist in the world.

DAN CRANE: I’m Dan Crane, and yes, my claim to fame, if you can call it that, is that I nearly, but not quite, won the World Air Guitar Championships, which is a thing, that exists, and has taken place annually in Finland for more than two decades. But this is not a podcast about the intangible art form slash sport of competitive air guitar. Who would want to hear that? Trust me, about five people. And they all still live in their parents’ basements. No, this is a podcast about what I discovered when I started looking into how worried I should have been about that burning light on the horizon. Because the thing that I found when I looked into wildfires was: soil.

This show is called “The Thin Layer” because, when we were making it, we kept coming across this idea that “man has only a thin layer of soil between himself and starvation.” And yeah, we do. There’s a hell of a lot of other things that rely on the thin layer of soil that wraps around the Earth, as well, and over these five episodes, I’ll be taking you on a journey through exactly how incredible those things are.

But let’s back up a second. It’s December 2017, and there are wildfires ravaging Los Angeles — my city — and this is what I keep hearing.

KCRA NEWSI ask you to be patient. You’re going to enter a different kind of danger zone when you go back home. That danger may lie in the rubble they’re returning to. Health officials are declaring a public emergency, asking homeowners not to sift through ashes once they do go home.

KPIX NEWSNow the main concern is the unknown toxins in the ash. Things like solvents, pesticides, household cleaners.

DAN CRANE: In addition to my prowess in nearly winning competitions in which people drunkenly pretend to play the guitar, I’m also a journalist, and have written for the New York TimesWall Street Journal, and lots of other places. Soil’s been on my radar for a while, as one of those topics that keeps surfacing (no pun intended) during my work. But in December, soil was a place where toxic ash from wildfires was ending up, right by where I live. Soil became personal. And, as a journalist, hey, I love a hot topic. (Pun very much intended that time.)

VICTORIA BALFOUR: Hah, why, why do I care so much, about ash?

DAN CRANE: This is Victoria Balfour. As she mentioned, she cares a lot about ash. She’s a post-wildfire hydrologist — a researcher in how water behaves when it flows over landscapes recently ravaged by wildfires.

VICTORIA BALFOUR: Oh man, that what is a big question. Well I’m a big proponent that wildfires are one of the coolest things ever, and actually incredibly beneficial for our ecosystem. And it’s something we’ve tried to control, and kind of made worse.

DAN CRANE: “Water flowing over landscape” sounds like the title of a lovely painting by Monet, but in southern California recently, it’s meant devastation. This is a seasonal occurrence in places like California — wildfire season leading into mudslide season. There was a horrific debris flow in Montecito, a town just north of Santa Barbara, in early January, killing 20 people, that came from a combination of extremely unusually bad weather happening in sequence: the second-driest December on record, then the biggest wildfire ever recorded in California history, then a truly exceptional amount of rain hitting the mountains overnight on January 8th.

What normally happens on mountains when it rains is exactly what you’d think. You get rivers, streams, creeks. But the thing about hills and mountains and sloping land is that a lot of the time it’s held together by plant roots. Burn those plants up, and then follow it with some heavy rain, and you get exactly what happens when you’re a kid pouring a bucket of water onto a sandcastle. There’s nothing keeping the land together, and the surface slips and washes downhill.

But it’s not just the devastation of a mudslide that’s concerning — I mean, it’s obviously very concerning if the mudslide threatens or actually destroys your house. But what’s even scarier is what happens to the mud as it travels over miles of varied terrain.

VICTORIA BALFOUR: When we had those massive wildfires happening down in California, it kind of completely changes the game, especially with, at least, you know, my speciality, which is ash, and you have to think about, ash is just really created by thermally degrading anything. You’re degrading it down into it basic elements. So something that might have, like a paint that might have lead in it, all of a sudden you’re going to get this high concentration of lead in your ash. So when you start consuming or you can start burning urban structures, there’s so much more toxic material in urban structures, not necessarily in the wildfire, and then this ash is very, very easy to move, through water, through wind, it can be inhaled.

DAN CRANE: And the wildfires last year in southern and northern California meant that this was a huge problem for people who, naturally, wanted to return to the ruins of their homes and search for their possessions. And aside from the tainted ash polluting rivers and water supplies, it also contaminates mudslides and debris flows because it’s in that mud. And once the mud settles, it’s still toxic, whether it’s left where it first settles, or is dug out by municipal workers to take somewhere else during a cleanup.

VICTORIA BALFOUR: I think a good analogy too for what we’re dealing with with wildfires is no different from, you know, floodplains, or earthquake zones. But it’s the first time really in our society that we’re really butting up against this new kind of natural disaster. And it’s one because we’re moving more into the wilderness areas where these fires happen, and these fires are also getting bigger and harder to control.

DAN CRANE: Let’s say that last year’s wildfire season in California — which was in October in the north, and December in the south where I live — the total area burned was about three-quarters the total size of the state of Rhode Island, and a lot — a lot — of that land is where people lived. Don’t mistake the glamor of LA and the famous celebrities fleeing the fires as a sign that this is just something for the rich and wealthy to worry about, either.

VICTORIA BALFOUR: It’s something that we’ve kind of tried to control and and now we’ve made a lot worse, but wildfires happen, it’s just kind of nature’s way of cleaning out debris and disease and reinvigorating the ecosystem with nutrients and life. As much as I admire Smokey the Bear, I am a big proponent that he’s one of the worst things that ever happened to the United States’ forests.

DAN CRANE: Right, Smokey the Bear, for those of you who are unfamiliar with his cute hat and blue jeans, was a mascot for a five-decade-long campaign to educate the U.S. public about the dangers of forest fires.

SMOKEY THE BEAR CAMPAIGN ADIt only takes a careless moment to turn this… into this. Don’t let forest fires be your fault. Make sure your fire is dead out. Remember, only you can prevent forest fires.

DAN CRANE: Since the start of Smokey’s reign, which began in 1944, forestry officials have worked to extinguish any fire as soon as possible. But that’s not how nature works — most forest ecosystems need periodic fires, in the same way that your house needs to be cleaned up from time to time. As a result of this policy, huge quantities of highly-flammable material have built up in many of the nation’s forests. So when a fire does happen, it has the fuel to grow and spread far and fast, destroying anything in its path. That’s one of the reasons that many people over the years, including Victoria, have argued that forest fires should be seen as a good thing, and that campaigns like Smokey’s have instead exacerbated the problem.

In building up against more and more land at risk of regular wildfires, and suppressing those fires to protect ourselves, we’ve ended up making the problem even worse — twice as much land burns each year in wildfires now as it did thirty years ago, in California.

In her research in areas of Montana hit by wildfires, Victoria has studied the interactions between ash, soil, and water, and began to see wildfires as a kind of creation as much as a kind of destruction:

VICTORIA BALFOUR: I love just how water is such a powerful element that can change our landscapes. I just picked up this field job, to get out and get some money, and it was on this post-fire hydrology project — and I’d never heard of any research like this or I didn’t even know what post-fire hydrology was — and I just went out and I was helping out in the field and I just instantly was in awe of wildfires. Just, the fact that you could walk into a post-fire landscape, and so many people, even myself in the beginning, you’re just, you’re kind of crushed because you just see all this devastation. And then to start learning about all the beautiful things that are happening, about all this regrowth, about how there’s so many benefits associated with wildfires, and for the ecosystem.

DAN CRANE: Because that’s what’s meant to happen, right? There’s a fire, and then there’s ash, and the ash mixes with the soil, and the soil is rejuvenated by the ash, new things grow, the circle of life, and so it goes. But it’s way more complex, way weirder than that, in nature.

Like, ash and soil don’t just mix together neatly. There are chemical reactions involved.

VICTORIA BALFOUR: And so when you burn something, it can have organic carbon and then it starts to thermally degrade as you burn it more and more, or higher temperatures I should say. And then it becomes carbonate.

DAN CRANE: Alright, we’re going to go science-y for a second here, a little, you know, throw some words at you you probably heard in high school, but don’t worry, it’ll all make sense. A carbonate is a molecule made up of hydrogen, oxygen, and… carbon, so carbon reacting with the air, pretty much. Like, baking soda is bicarbonate of soda, but there are all kinds of carbonates. The one that Victoria studied, in the wilderness of Montana, would be completely mundane if it wasn’t forming, by itself, in the middle of nowhere, when rain falls on new-formed ash.

VICTORIA BALFOUR: Or if you have like this very light rainfall event, it will actually hydrate that ash, and turn it back into calcium carbonate. To relate it to something else, an analogy, that’s exactly what we do when we form cement.

DAN CRANE: Sometimes, you get forests that catch fire, then pave themselves over…. With cement.

VICTORIA BALFOUR: Isn’t it crazy? It’s so cool.

Cement crust in a self-paving forest, post-wildfire, in Montana.


Cement crust in a self-paving forest, post-wildfire, in Montana. Image credit: Victoria Balfour

DAN CRANE: It is cool, that’s why we threw that little bit of science at you, see? The crusts help protect seeds, microbes, worms, bugs, even small animals, so that when the fires die down, there’s still something alive to bring the surface of the forest back to life. They’re even part of why mudslides are so dangerous after fires as well, because, well, we’ve all seen what happens to steep roads on hills and mountains during heavy rain. That water can’t seep and soak into the ground, so it has to flow downhill until it can find a place where it can.

VICTORIA BALFOUR: And I was so excited to actually document it in the field because I feel like people thought I was crazy. I mean, for years and years I’m collecting all these different ashes from all over the world, and trying to figure out what they are and how they’re different, and I’m in the lab and I’m like, I’m able to do this thing, this thing has to be able to be done out in nature too. I think it was the point when I really realized I was a dork. You know? [Laughter] I’m like, nobody else can be as excited as I am about this little thing right here. And the people in the field working with me, the field hands are like, OK, what is it? And I’m like, you don’t understand, this is like the holy grail right here.

DAN CRANE: Alright, so if you’re as excited by this as Victoria — and hey, you do you — we have got a picture of some crust on our site. Yes, actual crusts, check it out.

Self-paving forests have been around, undoubtedly, as long as there have been wildfires, but we only discovered them a few years ago. That’s what I soon discovered, looking into this — it is ridiculous how little we know and understand about the ground beneath our feet.

There are all kinds of complex, interlinked environmental cycles like this that we’re only just beginning to grasp — that I’m only just beginning to grasp, in truth. But the journey for me, from standing on my porch wondering about what’s happening on the horizon, to now, involves a pretty severe perspective shift.

So, those fires that were almost as big as Rhode Island. They’re happening because the climate is getting warmer — and I noticed them because they directly threatened me and my family. If you head north a bit you get to Canada, Alaska, Siberia, those kinds of cold places where there aren’t many people living and there are way more trees, wrapping their way around the northern subarctic part of the world like a headband. The fires there are even bigger. Canada had one last year about half the size of Israel. Russia had one in 2012 that was as big as Colorado or the United Kingdom.

Here in California, I’m having to worry about ash that’s full of toxic chemicals and poisons and heavy metals moving around, but all these bigger fires, up north — they happen every year, and they’re also getting bigger, and there’s a hell of a lot of ash being thrown up into the air as a result. It might not be toxic ash, but it’s still a lot of ash. And things that happen in one place, don’t only happen in one place.

There’s this dried-up lake bed in Chad, the Bodélé Depression, that perfectly illustrates what we’re talking about here. Until about a thousand years ago, it was part of one of the largest lakes in the world, about as big as the state of California. Then, it started drying up, and receding, and receding, as the climate warmed slightly and the Sahara grew southwards. Pretty soon, only a small corner was left, today’s Lake Chad. The rest of its sediment was now exposed dirt, left to bake in the sun.

By a quirk of geography, there’s a break between two mountain ranges which lines up perfectly with a long, thin strip of land in the Bodélé Depression — and if you fly overhead on the International Space Station — which I do all the time — you’d see what looks like a kind of natural wind tunnel, where the wind rushes through, kicking up dirt and soil. It goes up into the air, where small motes of dust are light enough to be carried straight out over the Atlantic Ocean. And it goes on, and on, and on, for ten thousand miles, until much of it lands in the Amazon.

We’ve known about this phenomenon for a long time, but it was only recently, in 2015, that we realized how exceptional this form of trans-Atlantic flight was. That it was actually one of the most important accidents of geography in the world. Those lush, Amazonian jungles — the “lungs of the planet”, the most diverse ecological environment in the world — those plants and trees are only so lush because they get this regular booster shot of fertile soil from across the sea. The equivalent of seventy-four Empire State Buildings’ worth of dirt lands in the Amazon every year, according to NASA. We know from sampling the air in the Amazon what else falls there every year, too: smoke, dust, spores, artificial aerosols, bacteria, fungi, pollen. The Amazon’s breathing the same pollution, the same everyday stink, that we do.

Imagine Greenland — the large white island on top of every world map. It’s white on those maps because it’s meant to be covered in ice, up to two miles thick at its thickest. It’s the second-largest ice cap in the world after Antarctica. And ice and snow… is white, right?

Not always. That’s where the ash is going from those huge fires, in Canada and Alaska and Siberia, as well as all kinds of other byproducts of human civilization — just like in the Amazon — from all over the world. For centuries, humans have benefited from natural quirks of wind and geography, like the dust from the Bodélé Depression fertilizing the Amazonian rainforest like a weightlifter on steroids, growing larger than it ever could have otherwise. Now, human civilization has advanced to a point where we’re powerful enough to create our own globe-spanning climate quirks.

Now, go to Greenland today, and things are changing. Pass the small fishing villages perched on the thin strip of land around the southern edges, where humans can carve out survival against intense cold. Go inland, and there’s a lot less white than there used to be. There are large, growing patches of “dark snow”. It’s dark because of ash and soot. One patch alone in western Greenland is about as big as West Virginia, it’s getting bigger every year, and it’s not the only patch either.

You see, as every goth on a summer’s day knows, dark colors absorb much more light than lighter ones. Places like Greenland are meant to go through periods of waxing and waning, getting larger or smaller with the seasons, and normally there’s a lot of dust and other small things, carried on the wind, landing there. The reason we can use ice cores from Greenland to study how the Earth’s climate looked in the past is, in part, because there are tiny layers of dustfall trapped in there, just like rings in a tree. And it can come from wherever — a lot of the dirt that ends up landing on Greenland each year naturally comes from the deserts of Mongolia, for example.

But here’s a really weird thing. That dark snow? It’s also alive, and it’s eating Greenland. It’s also algae. Spores are small enough to be blown here with the ash and dirt, and then when they land on the exposed, melting ice, the ash and the ancient sediments exposed by melting make for a delicious meal. They also generate a kind of dark-colored pigment to protect themselves from the harsh sunlight on the exposed surface of the ice — the pigment makes the snow even darker, it melts even faster, and… you get the picture.

This is the perspective shift I was talking about, going from my porch to something bigger. I’m starting to understand that talking about dirt or ground or soil or ash or soot in isolation doesn’t really make sense — not only does the point where one of those things ends and another begins totally depend on context, but it also makes so little sense to talk about dirt as something sterile, something that just… exists.

It’s full of life, and that life is shouting at us to pay attention to what’s happening.

ELIZABETH BACH: Many of the North American ecosystems, fire has been a regular part of those ecosystems either naturally through things like lightning strikes or, for centuries, by management, for the native peoples who lived here. And so many of these systems have evolved with fire, and there’s many kinds of plants that actually require some fire to reproduce or to, to be healthier, to continue growing well.

DAN CRANE: This is Dr Elizabeth Bach, the executive director of the Global Soil Biodiversity Initiative. Her research is on grasslands — thinks prairies, savannah, steppe, those kinds of places — but Dr Bach’s work isn’t on plants, primarily, though — it’s on dirt. Wait, not dirt, sorry.

ELIZABETH BACH: For me the difference between dirt and soil is that soil is alive.

DAN CRANE: Yeah, this is important to keep in mind — soil is alive. Just as much as the plants growing in it. And, as you may remember from The Lion King, there’s a circle of life. Plants and animals are born, they grow, they die, and the next generation lives on their remains, whether it’s eating a dead animal or eating a plant that’s growing in the remains of other plants or animals.

ELIZABETH BACH: Soil is really a mixture, a matrix of mineral components, of broken down pieces of rock.

DAN CRANE: The dead stuff from plants and animals mixes with the rock, and it all sticks together into clumps by static electricity. Air and water flows through the gaps. And there’s also other stuff like magnesium, calcium, iron, manganese — all the kinds of elements you find in your average Flintstone’s vitamin for humans. Then there’s carbon, too, which is used for energy. Now, there’s actually about four times as much carbon in the soil as there is in the atmosphere — it’s one of the main places carbon is meant to hang out when it’s not a gas, when we’re not busy burning fossil fuels or starting wildfires, for example.

And in among all that, there’s also life.

ELIZABETH BACH: More than 25 percent of total global biodiversity lives in the soil. It’s a, it’s a tremendous reservoir of living organisms that we often don’t think about.

DAN CRANE: There’s fungi and bacteria, and viruses. There are worms , and there are insects too, of course. The smallest stuff, the spores and other microbes — any time that soil moves, like blowing halfway across the world—it takes those tiny aeronauts along for the ride.

This is all meant to be a normal part of what makes the Earth so full of so many kinds of different forms of life, where you have these chance coincidences that mean life on one side of the planet sustains life on the other side. But at the center of this web of interconnecting life and dirt, there’s soil. And we’re ruining it. Everything around you, and everything you do? Yeah, you rely on soil not screwing you over.

DIANA WALL: We depend on soil for our air. Clean water. The food we eat. And so to not have it means that human society is limited.

DAN CRANE: This is Dr Diana Wall, a colleague of Dr Bach’s. She studies soil in Antarctica, one of those places where we can see the world changing at its fastest, and she — among a huge number of other roles — is the founding director of the School of Global Environmental Sustainability at Colorado State University. She’s been honored a number of times for her work in Antarctica, which, according to her Wikipedia page, she’s visited 13 times…

DIANA WALL: Well I don’t, I don’t even know I had a Wikipedia so, [laughter], that’s kind of interesting. I wonder who did it?

DAN CRANE: She’s actually been to Antarctica so many times she can’t even remember.

DIANA WALL: Well, it’s a lot, you know, you just get hooked, just get hooked. But I think that we worked in the biggest uh, arid, what do you call it? Ecosystem, terrestrial ecosystem there is in Antarctica.

DAN CRANE: That “biggest arid terrestrial ecosystem in Antarctica” is the McMurdo Dry Valleys, the largest ice-free area on the continent. Sheltered from encroaching ice by surrounding mountains, the valleys are located far south of New Zealand, and not so far west of McMurdo Sound, where the largest permanent Antarctic base is. Wall has done so much work in the Dry Valleys that one even bears her name: Wall Valley.

Even in Antarctica, the soil is alive. Dr Wall studies nematodes — roundworms that range in size from the microscopic to the visible, which are everywhere. 80 percent of all individual animals on Earth are estimated to be nematodes. That’s crazy. 80 percent of all individual animals, on Earth. But Dr Wall’s work is part of a network of scientists whose research is reacting to a changing world, and trying to figure what the hell that means for the world beneath our feet — and what that mean for us.

DIANA WALL: I think climate change is the biggest threat because we don’t know what’s happening above and below ground, and they’re connected. That’s the thing we, we forget, you know, it’s not like a soccer field where you just cut it off and there’s, nobody worries about what’s below ground.

DAN CRANE: And even when we do worry, we don’t understand fully what’s happening beneath our feet when above ground conditions change — nor how change in one area can be felt elsewhere in the world.

DIANA WALL: I think climate change, we know because it’s the community of plants above that, with the geology of the soil below, or the soil chemistry below, has created that habitat. So if you move that plant, or an alien plant comes in, what happens below? So I think that’s really a, a crucial unknown, is what happens a lot with these alien species. Then I think, you know, there’s just the practical things we’ve been dealing with forever that you may want to call land use change, but I just call it pollution, you know? Killing them off and we don’t know what we’re killing or whether this is going to be transported by wind or water and whether the organisms are going to be transported. Some of these organisms are small enough they can be transported like, like spores.

DAN CRANE: Dr Wall’s experiments are seemingly simple — a lot of them involve hiking out into the Dry Valleys, putting domes over patches of land, and then adding more water, or more carbon, and seeing what happens to the cold desert ground of Antarctica. Climate change means that the poles might get wetter as well as hotter, we’re not totally sure yet. That might mean more carbon in the atmosphere, and it could even mean more weird effects — weird in the same way that it’s weird you sometimes get forests that pave themselves over with cement after a fire. Here’s Dr Bach again.

ELIZABETH BACH: Permafrost is a great example of this. They tend to be waterlogged or frozen, so there’s not a lot of oxygen circulating through that system.

DAN CRANE: Without oxygen, the microbes in frozen soils have to breathe differently to survive — they steal the oxygen atoms from carbon dioxide instead, and end up exhaling methane.

ELIZABETH BACH: And so this methane is accumulating, but because the soils are frozen, particularly on the surface, that methane just gets trapped there. It never diffuses on up into the atmosphere, whereas a soil in a temperate area, that diffusion can just happen.

DAN CRANE: There’s this bizarre video on YouTube from 2016 of Russian scientists working on an island off the north coast of Siberia — in seas often covered in ice. In the video they’re bouncing up and down, like on trampolines, but it’s not a trampoline — it’s melting tundra. Ice takes up more space than water, so as permafrost melts, the methane is released and the land develops these huge pockets of trapped gas. You can make the Earth burp, or fart I guess, by jumping up and down on them.

ELIZABETH BACH: And so as we see melting the permafrost, these little methane bubbles that have been trapped, you know, probably for decades or sometimes centuries are having, are finding their way towards the surface and creating these kind of large pockets. And then when that melts, these large pockets just kind of burp up into the atmosphere.

PAUL BOGARD: It’s very scary — and when I spoke to the scientists who were studying this stuff, they are really worried about it, nobody, it’s one of those things where nobody really knows what it all means and it’s happening slowly.

DAN CRANE: This is Paul Bogard. He wrote a book in 2017 called The Ground Beneath Us — it’s about how we need to start paying more attention to what’s been happening beneath our feet.

PAUL BOGARD: Well, I remember talking to a scientist who said, you know, all of our estimates about, you know from the IPCC for example, on climate change and kind of where we are now and where we’re headed, none of them include this thawing permafrost. And when you start to factor in what would happen if the permafrost thaws and releases, as it’s doing, and releases the greenhouse gases what it holds, those estimates for where we are and where we might be headed, just, they’re thrown out of whack.

DAN CRANE: Well that’s reassuring, no?

PAUL BOGARD: This seems like something that should be being discussed on the floor of the US Senate right now, like, what are we going to do when this happens? And yet it’s something we… you want to talk about being oblivious to the ground at your feet? This is ground that we are just completely oblivious to, and it has the potential to wreak havoc on the planet.

DAN CRANE: And not to be too doomsday about this, but… temperate soils, the kind of soils you get in your backyard, or on a farm — they’re not doing so hot either. Take farming. You take a plow, and you dig up the soil, breaking it up into finer particles so that you can plant new seeds in it while also removing roots and weeds.

But when you do that, you’re opening up the soil below ground to a lot more oxygen. And just as too little oxygen in the tundra leads to giant methane trampoline burps, too much in the landscape that are heavily altered by humans can also have consequences. Here’s Dr Bach again.

ELIZABETH BACH: So as you increase that oxygen availability, all of a sudden the soil organisms can just eat, eat, eat, eat, eat.

DAN CRANE: The microbes in the soil are being allowed to convert the material around them into air, just like the algae in Greenland, giving too much food sets off another kind of feedback loop.

ELIZABETH BACH: And so in a place like Iowa where I grew up, the soils of Iowa have lost an estimated, somewhere between a third to a half of their organic matter, has essentially just been respired away in the past 150 years.

DAN CRANE: And the most incredible thing is… life on Earth, including our own, depends on how we treat these microbes, but we’ve barely scratched the surface — apologies to the pun-averse — on the diversity of what lives in soil. Paul Bogard.

PAUL BOGARD: I remember when I was interviewing a scientist at the University of Colorado Boulder and he likened our knowledge of the, of soil microbes to essentially the knowledge that Thomas Jefferson and Lewis and Clark had in 1805 about the western U.S., you know, we just, they had no idea what they were going to find out there.

DAN CRANE: Perhaps we should label maps of the world with big monsters and giant squids, over big patches of empty land, like old cartographers unsure about what lay at the edges of the world.

PAUL BOGARD: They had no idea what they were going to find out there and they imagined that there might still be mastodons roaming, saber tooth tigers and that kind of thing, just this vast terra incognita, this unknown land. And that’s where we are today in 2018 when it comes to understanding microbes in the soil. There’s just, we just don’t even know what’s in the ground below us.

DAN CRANE: And everything does depend on soil. Soil isn’t just dirt. There are more microbes — bacteria, fungi, and more — living in a handful of soil than there are stars in the galaxy. Every field or forest has a universe of its own, beneath our feet, invisible to the naked eye, but keeping us alive by regenerating and revivifying itself, over and over again. We grow our food in soil, we build on it, and pretty much every antibiotic we’ve ever found was first discovered in soil as well. We bury our dead in it. Ashes to ashes, dust to dust.

Yet while in plenty of places the world’s topsoil goes quite deep, there are also plenty of places which seem like verdant, healthy grassland or farmland, but where the soil’s only a few inches thick — only a few inches between our feet and bedrock. Yet within that narrow, thin skin is pretty much everything that sustains and drives life on Earth.

PAUL BOGARD: I stumbled across a statistic that wowed me, which is that in the States and in Europe people spend between 90 and 95 percent of their time inside now. So in their houses and their places of work and their cars, you know, we’re just, we’re almost always inside. And I started to think that for most of us, even when we walk outside, we walk on pavements and it really spoke to me of how we become so separated from the ground at our feet. We just, we never touch our feet to soil, we never touch our feet to natural ground.

DAN CRANE: This has been the first episode of The Thin Layer. Over the next four episodes, we’re going to be looking at some of these stories of soil — stories about how everything we know sometimes comes down to the stuff stuck to the bottom of your shoe.

I’m looking down a lot more now. Are you?