“My favorite is Martian soil, above Moon soil, because the Martian tomatoes tasted a little bit sweeter. Some people like it a bit more spicy and then they have to go to the Moon because on the Moon soil simulant, it tasted a bit more spacey… uh, spicy.”

In warehouses, bunkers, basements, and skyscrapers, urban hydroponic farms produce food without soil at all; meanwhile, exobiologists are inventing ways to grow food among the stars.

In our final episode of “The Thin Layer,” we ask: in these futures, is there still a place for soil?

Presented by Dan Crane
Written by Ian Steadman & Eli Lee
Sound design by 
Laura Irving

Made with the support of The Bill & Melinda Gates Foundation

Featured guests

Music & audio credits

  • Theme tune // Dan Crane
  • “They Call It Nature,” Raise Your Hand If You Think Evil Is Increasing in This World”(edited/re-versioned excerpts, from It’s A Wonderful Jaws) // Chris Zabriskie
  • “Leela,” “Purple Light,” “They Call it Nature,” “Ratchet Up,” “Galaxy Shard,” “Veins of Silver” (edited/re-versioned excerpts) // Blue Dot Sessions
  • Belong To Moon” (from Dog and The City) // Martin Rach

Show notes

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

A render of a greenhouse on Mars. Image credit: NASA
Flowering plants growing in Martian soil simulant. Image credit: Wieger Wamelink
  • Hollywood may not care too much for the detailed science of growing things in space, but it’s a common subject in some corners of sci-fi. Andy Weir’s novel The Martian, the source for the movie of the same name, is one such example. For an idea of how the ideas of writers like Arthur C. Clarke have had direct influence on NASA’s real-world innovations—especially when it comes to growing and/or eating food—this piece by Matt Novak at Slate is a good start.
  • More info on Wieger Wamelink and his team’s research into turning simulated Martian and Lunar dirt into soil, using earthworms.
  • Growing Underground has a promo video that shows off their grow setup:
  • Stan Cox in Salon gives an overview of the limitations of plant factories, “vertical farming” (skyscrapers where every floor is a farm like Growing Underground), and other futuristic proposals for urban agriculture.
  • This Tiny Country Feeds The World”—a National Geographic profile of Wageningen University, and its role in turning the Netherlands into the world’s second-largest exporter of food by value.
  • Hi-tech greenhouses in Norway are being used to grow fresh vegetables year-round, above the Arctic circle.
  • Wired looks at “the surreal sci-fi farms that grow most of our food.” Shows just how controlled and technologically-mediated modern agriculture is, even when growing in soil.
  • Here’s a fly-through of EDEN-ISS, the greenhouse that might actually be built on Mars some day:


DAN CRANE: If you believe the movies, space colonization is kind of straightforward: you send out a bold adventurer. They set up a base in a hostile environment, and start making a small corner of a new world habitable. There might be hostile aliens hiding in the shadows, sure, but actually building a base on a new world seems to be the easy part.

Those kinds of movies omit an important detail, though. I mean, if I went to live on another planet, the first thing I’d be asking is, where can I get a cup of coffee? And then, what’s for dinner? Okay, maybe not the first thing, there’d be lots of ooh-ing and aah-ing for a good few hours after I got off the shuttle and walked around, but after a while, even if you’re on another planet, you still gotta eat. That makes for less compelling cinema than shooting green bug-eyed monsters, but still, growing food on another planet? That’s actually going to be a hell of an adventure some day.

Welcome back to The Thin Layer, the podcast about dirt, with me, Dan Crane. It’s our final episode, and after talking a lot about earth — the crumbly dark kind — get ready to go on a journey, far, far away. Because today, my friends, we’re going beyond soil.

There was one recent movie that approached settling another world in a mostly-scientific way — Ridley Scott’s 2015 film The Martian, about Matt Damon’s character Watney trying to survive, stranded alone on the Red Planet, until NASA can send a rescue mission to save him.


DAN CRANE: The challenges of growing without soil somewhere like Mars aren’t actually that radically different to trying to grow food on Earth in places like deserts. Earth has soil, Mars just has sand and grit. It’s not exactly blooming, and, as far as we know, there’s no microbial life on Mars either. The life that makes soil, soil. A lot of it’s iron oxide, or rust. Hence the “Red Planet.” The Martian’s solution to growing in the lifeless dirt is to get Matt Damon mixing some of it with his freeze-dried poop — it’s just manure, after all. And it works. He grows potatoes.

MATT DAMON: All right, let me get a few things out of the way, right off the bat. Yes, I did in fact survive on a deserted planet by farming in my own s**t. Yes, it’s actually worse than it sounds, so let’s not talk about that ever again.

DAN CRANE: I think he deserved an Oscar for that. In any case, while I’m not saying that all we need is enough poop and we could turn that red, dusty dirt of Mars into fertile, bountiful plains, what I am saying is that the idea that you can grow food without soil here on Earth — the soil that, we’ve come to learn, is an absolutely essential part of our planet-wide ecosystem — is not entirely dubious.

The reason we called this show The Thin Layer was because, during our research, we came across an old saying. Quote, man has only a thin layer between himself and starvation. End quote. Soil is a delicate, precious thing, and it’s under threat in a lot of different ways. But there’s also hope. There are ways to regrow dead land that’s turned to desert. There are ways to change how we farm to limit erosion, and to stop killing the microbes that form a crucial part of the global ecosystem. Yet there could be a point where we need to think outside the box — when the impact of climate change and population growth means that we need to get inventive, ambitious, even ingenious. After all, if we can grow food up there among the stars without any soil at all, then surely we can do it down here as well.

For this, our final episode, we want to ask two simple questions: Can we ever get beyond soil? And if so — should we?

WIEGER WAMELINK: My favorite is Martian soil, above Moon soil because in my belief, and I must say in my belief, especially the Martian tomatoes tasted a little bit sweeter.

DAN CRANE: Wieger Wamelink [Vee-ger Vama-link] is a Dutch ecologist and exobiologist. The exo stands for “off-Earth.” He’s figuring out how to grow food on other worlds.

WIEGER WAMELINK: Some people like it a bit more spicy and then they have to go to the Moon because on the Moon soil simulant, it tasted a bit more spacey… uh, spicy, especially, and spacey as well, by the way.

DAN CRANE: With his team at Wagenigen [Vaga-ningen] University in the Netherlands, he’s been bringing science fiction to life, growing crops in soil from the Moon and Mars. No, wait, let me explain, he’s not using actual soil from Mars and the Moon; they use what’s called “soil simulants,” close analogues to the dirt you’d find there. And in these simulant soils, Wieger and his team have been experimenting with growing tomatoes, green beans, peas, arugula, and the Matt Damon-approved celebrity of Martian crops — the potato.

But, alright, let’s take a step back. How do you even simulate Mars or Moon soil on Earth? Step one — get your rocks:

WIEGER WAMELINK: We order it from NASA. But what they did, NASA, is based on all the measurements they have, both of the Moon and Mars, because, well, we’ve got the rovers running around there, doing samples, analyzing them in the laboratory that’s on board, so we know exactly what the minerals that are in the soil, we know exactly how that is.

DAN CRANE: Knowing the mineral composition of the space dirt in question, NASA could then track down a close analogue, something on Earth that has the same mineral makeup. Weirdly, they found their Mars soil only a few hours away from where I live in Los Angeles:

WIEGER WAMELINK: What we’re using at the moment is the next generation of Mars soil simulant, and that originates from the Mojave desert in the States as well. And well, that’s over 90 percent the same as what you would find on Mars.

DAN CRANE: I always had a feeling about the Mojave Desert, you know. Not enough of a feeling that I’d spread some freeze-dried poop over a square meter or two and then try to plant some vegetables, but it has always seemed a little… alien. And if you want to grow on the Moon, that’s no problem either. There’s a volcano in Hawaii that NASA gets its Moon soil simulant from, too. They collect rocks, and then put them into vacuum chambers, where they’re smashed into tiny pieces with fast-moving ball bearings. Wash it down, sterilize it, and you’ve got yourself something as much Martian or Lunar as the real thing, more or less, and with most of the nutrients — like potassium, phosphorus, and more — that plants feed on.

So, that’s the start. But one of the big differences between Martian dirt and Earth dirt is that Martian dirt has chemicals in it called perchlorates — a compound of chloride and oxygen. You can use perchlorates in explosives or rocket fuel or cleaning products, but they are extremely toxic. Back in 2008, NASA’s Phoenix lander found perchlorates in a dirt sample on Mars. Then another. And then another. Later missions like Curiosity have found that perchlorates are everywhere on Mars, and you cannot grow crops in dirt that has perchlorates in it. Even if they don’t kill the plants, those plants will absorb them, and they’ll travel up the food chain and into us.

Matt Damon doesn’t have to deal with perchlorates in The Martian because, well, no one’s entirely sure that there’s a way to easily wash them out of the dirt, plus they’d get in the way of our story. But that said, NASA thinks it’s not an insurmountable problem. Perchlorates might only be present in the top layer of soil, too, which would just mean digging down into the ground a little more to get to the safer dirt. Wieger has his own proposed solution, as well:

WIEGER WAMELINK: Perchlorate, it also occurs on Earth, not in high quantities in the soil, but it is present and there are bacteria that break it down. So if it is there, we could solve it, and we are already working on that. Bacteria break it down into oxygen and chloride, eh? It’s the same chloride that you find on the beach, the salt, that’s what you taste. So that’s already better. But chloride itself is also a problem for plant species. But, well, actually I’m looking at the plants now, they’re standing in my, in my window tile, they’re salt-loving plants and you can use them to remove the salt from the soil. So that would be an extra phase in my system, but you could do that. You can eat it, and you can get it into your salad, and it will taste a bit salty. So you can eat it, and you can remove salts from the system. So, for me, it’s solvable.

DAN CRANE: Alright, thanks Wieger. So we’re getting there. Now, we can probably defeat the toxic chemicals in Martian soil. What’s next? Well, worms. Not to be underestimated when it comes to the future of the human race, although, this time, not the dancing, parasitic worms that we looked at in an earlier episode. Earthworms are the kind of life we need in space for turning dirt into soil. When they dig burrows, it helps water and oxygen circulate below the surface. And when plants die on the surface, earthworms chew that organic matter up and, well, deposit it behind them, along with colonies of microbes that can themselves start creating a new soil ecosystem. They’re tiny little Matt Damons, each and every one of them. Just cute little Matt Damons wriggling along in the soil. Lights, camera…

WIEGER WAMELINK: Yeah well, especially in the beginning, the most important thing will be human feces. So, poo.

DAN CRANE: Anything for the survival of the human species, Wieger.

WIEGER WAMELINK: Traveling to Mars will take over half a year and, well, you have to keep your poo, and keep it safe, and when you arrive over there then you apply that because there’s a lot of nutrients. It’s not that different from pig slurry or cow poo. So you use that to start your crops growing because Mars contains quite a lot of nutrients for plant growth, but one essential is missing or almost missing, and that is nitrogen in the form of nitrate. That is, if you buy manure at your garden center then always is also nitrogen included, in the form of nitrate. And that’s what plants need, especially to grow and to build all kinds of plant substances. They need quite a lot of it, and that is missing on Mars. And that’s also present in our poo. So by adding poo to the Martian soil that would help a lot, and would really start off, well, the plants growing over there, so that’s extremely important.

DAN CRANE: Wieger and his team have been letting worms live in some of their Lunar and Martian soils, and they’re actually the first researchers to get those worms to reproduce there. It prompts the question: Where’s the sci-fi movie where they send a giant spaceship ahead of us to Mars, packed full of poop and worms, to crash land into the surface and kickstart human colonization of the stars? Now, I would totally watch that.

But we’re getting ahead of ourselves. It looks like it’s maybe possible to take the sterile dirt of other planets in the Solar System and cultivate healthy, fertile soil. And the research that Wieger and his team are undertaking is the kind that can be used on Earth as well — they’re currently investigating whether they can turn a number of test sites in deserts in the Middle East “green” again. That’s one way to respond to the possibility of a world beyond soil — just create new soil, hitting a planet-wide undo button on environmental degradation.

That’s assuming that we always need soil, though. That’s why we opened this episode by asking that question: Can we ever go beyond soil?

DAN CRANE: That is a very old looking elevator. Alright, here we go. We’re getting in a very tiny little lift here. What, and what year would this lift date from?

RICHARD BALLARD: Uh, this would’ve been here from the start. I mean the engine and, and all that sort of stuff is obviously new. Yeah. But the, the actual lift shaft. So it’s, it’s two staircases, like a double helix, like DNA, wrapped around the central lift shaft. And the plan was to, we’ve got two of these staircases, one at each end of the tunnel, and there’s also a staircase that goes into Clapham Common station, which is now bricked off.

DAN CRANE: We can find one vision of a future without soil more than a hundred feet below the surface of London, in the United Kingdom.

RICHARD BALLARD: OK so, my name’s Richard. I’m one of the cofounders of Growing Underground. Growing Underground is an urban farm, it’s situated 33 meters under the streets of Clapham, London in a World War II air raid shelter.

DAN CRANE: This is me hanging out with Richard Ballard, who, with his partners, got planning permission in 2015 to turn this one-time bomb shelter into something completely unexpected: an underground farm. Where eight thousand people used to shelter from Nazi bombs, there are now rows and rows and rows and rows of plants, growing under artificial light.

RICHARD BALLARD: We use hydroponics and LEDs to produce microgreens, which are tiny herbs, packed full of flavor. We pack these on site and then we ship them into New Covent Garden Market, which is less than a mile away, and from there our produce is distributed over the capital to hotels, restaurants, and retailers.

DAN CRANE: Now, there’s a whole range of strong, strange lighting — bright white, washes of pink, and vivid violet, powered by renewable energy sources above ground. Here, crops can be grown in a controlled environment, unaffected by the weather or seasonal changes, and also, without soil. This could be the future. This is hydroponics.

RICHARD BALLARD: So we use coriander, pea shoots, rocket, fennel, wasabi, mustard.


RICHARD BALLAR: All different types of products.

DAN CRANE: And they never grow to full, but you’re only selling the sprouts at this point?

RICHARD BALLARD: Yeah. So we only grow to first true leaf, or um, sort of cotyledon stage of the plant, which is the first leaves coming out. This is where the plant is very small and there’s very intense flavors in it. So, um, as the, as the plant grows, for example, coriander, as it grows, the flavor dissipates. And you still have that flavor coriander, but when you have it in a small shoot and you have lots of them, the flavor’s really intense.

DAN CRANE: And I tasted a few, and it was quite delicious. And this bomb shelter, about half a square kilometer in size, produces around 44,000 pounds of salad greens every year. But let’s break it down — how exactly do they manage to magic all this up if they don’t have soil? First of all, the LED lighting has a big role to play.

RICHARD BALLARD: Currently, we use a little bit of the red spectrum, and a little bit of the blue spectrum, and some of it, in-between that, which is, like, the greens and the orange, which adds a flavor, but the light spectrum is, you know, you’ve got UV one, UV two, and the far red end, that, that goes further as well. So, we’re already, plants use a certain amount of the light spectrum, and what we’re doing now is giving them a broad light spectrum between certain parameters and that’s enabling to grow.

DAN CRANE: These are called “light recipes,” and as you can imagine, if you’re able to control the light, you can give crops exactly what they need — really finetune it — and only use exactly as much energy as you need and nothing more. Growing Underground uses fertilizers, too — the “standard NPK,” as Richard calls it, nitrogen, potassium, and phosphorus, and it’s pumped into water tanks that hold little floating pods, made of a kind of a sponge. This is what replaces the soil. Inside each of these floating pods is a plant, its roots grown out and dangling into the water. The fertilizer goes into the water and is sucked up by the roots. Everything’s fine-tuned there too, so each plant gets exactly what it needs in exactly the right proportions. It’s a great way to maximize productivity, and minimize waste.

Hydroponics can fit anywhere you can fit a fish tank — Ikea sells home hydroponics kits now, and plenty of people have been building DIY hydroponic gardens for years to grow everything from chili peppers to, yes, marijuana in wardrobes and cupboards. Why go for a boring old vegetable plot in the garden, why bother getting your hands dirty, when you can get a taste of the future, or a puff of the future, if you will, right there in your kitchen? Urban farms take this simple concept and scale it up — if you take empty urban spaces, like a World War Two bomb shelter, or a warehouse, empty lots or abandoned offices, you can turn them into a huge network of productive small-scale farms. Since you’re growing food in the cities themselves, where most people live, you cut down on food miles, it creates jobs… it’s an apparent win-win.

But of course, there’s a fly in the ointment, or, or a worm in the soil? No, that doesn’t work, that’s terrible. Have I finally run out of soil puns? Ah. In any case, there’s no way to get around it — Growing Underground, impressive as it is, isn’t going to replace your typical farm out in the countryside. There are limitations to this technology. For example: It’s all well and good powering your underground farm with renewable energy, but you’re underground. It’s fundamentally wasteful to take sunlight hitting a solar panel, transfer that electricity down to a bomb shelter, then reproduce that sunlight in an LED. You could just… I don’t know, grow above ground, use the sun. Growing Underground has enormous ventilation fans at either end of its tunnels, too, and keeping them running is expensive. Not to mention the old elevator that keeps breaking down. It’s better than having empty urban space going to waste, sure, but compared to actual farms, it only makes sense for a limited range of salad crops right now, both in terms of energy and in terms of the economics of having to produce and sell a harvest.

RICHARD BALLARD: So in the next 10 to 15 years you’re going to see an exponential growth in technology, light recipes that are producing, you know, a light spectrum perfect for a certain crop and, and then you’re gonna get some really amazing efficiencies with growing. And just technology in general is going to improve. The real game changer, really, is when we have cheap, abundant renewable energy and battery storage, and then we can start, you know, with that technological change and exponential growth in technology, we can start to produce the staples, like, you know, wheat, soy, maize, and other vegetables.

DAN CRANE: It’s for reasons like this that, while urban farms look great on paper, or in the pages of glossy design and architecture magazines, there’s a reason they’re almost exclusively used for growing salad greens for upmarket grocery stores and bougie restaurants for now. Those are the kinds of clients that can both afford the novelty, and demand the kind of consistent quality in flavor that a hydroponic farm can provide. The only exceptions are in extremely densely-populated countries without much farmland and high food prices already. The world’s largest indoor hydroponic farm is, guess where, Japan, where fresh fruit and vegetables are relatively expensive. There, so-called “plant factories” do look to make economic sense.

For the rest of us, this is only part of the future. It’s estimated that if we were going to produce the entire U.S. vegetable crop under electric light, it would take over half the annual electricity generation for the entire country. Just growing vegetables this way would generate 1.4 billion tons of carbon emissions, which is more than double what the entire U.S. agricultural sector already currently pumps out each year. So while there’s no technological reason you couldn’t grow a staple crop like wheat hydroponically, in economic and sustainability terms, it’s only a speculative possibility right now.

CECILIA STANGHELLINI: I believe there can be commercial value in some cases, but when people claim that the urban farm or plant factories will feed the planet in the future, I really get upset. It’s completely nonsense.

DAN CRANE: Cecilia Stanghellini is a horticultural researcher at the University of Wagenigen, in the Netherlands. She’s a colleague of Wieger Wamelink’s, although they work in different fields. Sometimes literally.

When it comes to the question of whether we can, or should, ever go beyond soil, Cecilia is one of those people directly finding out the answers. She is an expert on greenhouses, which might not sound like much, but, whether they use soil, or hydroponics, greenhouses are the secret to how we already feed much of the world — and how we might feed all of it in future, here or elsewhere in the universe.

CECILIA STANGHELLINI: I mean I have had people asking, well I’m going to build the plant factory, and then I said, okay, do you have enough electricity to feed the lamps? And they say, oh, we put panels, sun panels on the roof, and then you make a small calculation and you say, okay, you need not that roof but another one hundred roofs like that.

DAN CRANE: Now, here’s something completely amazing: The Netherlands is now the second-largest exporter of food in the world by value. This small country — which is only as big as the state of West Virginia — has completely reinvented how it gets food from farm to table, and Wageningen University is at the heart of that. They call the area around the university “Food Valley,” rather unpoetic riffing on Silicon Valley in the U.S., but it’s deserved. This is the epicenter of some of the most incredible food technology in the world. If you want to see beyond soil, if it’s even possible — Wageningen is where you need to go. (And if you remember Ken Giller and his projects to improve soil fertility in sub-Saharan Africa, from our last episode, guess what, he works at Wageningen as well.)

More than half of the Netherlands’ land is used for agriculture and horticulture, with crops growing in acre upon acre of greenhouses. They have climate control, LED lighting, hydroponics or soil or some combination of the two — but they’re far grander than urban farms. It’s made the Netherlands the world’s leading tomato producer, and the leading exporter of potatoes and onions. A third of the global trade in vegetable seeds is Dutch. In their intricately-monitored greenhouses, they can control every single production factor and produce yields way greater than you’d normally get on such small parcels of land.

What quality, quantity, direction, and colour of LED light will encourage tomato growth best? Which nighttime temperatures will make sweet pepper plants even sweeter? These are the kinds of questions Cecilia’s research is attempting to answer, fine-tuning food as much as possible. The type of greenhouse structure, the material it’s made of, how it shades or doesn’t shade what’s inside, its thermal properties, its heating and cooling systems, robotics, humidification, dehumidification — give me a second to take a breath here — CO2 enrichment systems, and optimization algorithms. Now, when I say finely-tuned, people, I mean finely-tuned.

But even here — even at the epicenter of global agricultural research — there’s still soil. Martian soil, Moon soil, Earth soil.

It’s not everything that it used to be, sure, but it’s still an important and vital piece of the overall puzzle. It’s a technological and scientific tool that’s still useful for solving large, complex problems. And as much as I keep talking about the future of food, this is also the present. We’re already living in a world where we’re pushing beyond the limitations of “just” sunlight and open fields.

CECILIA STANGHELLINI: In Europe, I think most people are really surprised when I say that no fresh vegetables that you buy in the supermarket in western Europe, and I would also say Britain, is field-produced. Tomatoes, field production of tomatoes is only for processing tomato, field production of sweet pepper has nearly disappeared. It’s because, because of the higher quality that you, of course rain is one problem, birds is another problem, and, and a closed environment makes it possible to have biological control instead of spraying chemicals. So increasingly, and it is mainly because of quality, and of course also productivity, vegetables for fresh consumption are produced in greenhouses.

DAN CRANE: Right now, Cecilia is involved in a European Union project to take how the Netherlands grows food, and trial it up in Norway, beyond the Arctic circle. It’s a place where you shouldn’t be able to grow tomatoes or potatoes, or, at least, not grow them well. But with this kind of controlled, intensive greenhouse technology, they’ve got Norwegian farmers growing as much food as Dutch ones.

CECILIA STANGHELLINI: Basically greenhouses are a solar collector. So if you manage it cleverly, there is enough energy, even without heating. The point is that energy up to now was so cheap that it didn’t make sense to invest in doing something better, but it is possible to do better.

DAN CRANE: Here’s what Cecilia says that the ideal greenhouse of the future will look like: It will have nearly zero environmental impact. It won’t need any fossil fuel energy. It will minimize its carbon footprint for its equipment. There won’t be any wasted water, nor fertilizers, and everything will be recycled. No need for pesticides, either. And all inside a sealed, artificial box. It doesn’t feel like a huge leap from the Arctic to Mars, does it?

What’s happening in the Netherlands is essentially turning the places we produce food on Earth into the same kind of closed-loop systems as spaceships — sometimes using soil, sometimes hydroponics, depending on the kind of plant production system we’re talking about. And Cecilia actually does apply her research to space, with a project called EDEN-ISS. The idea is to miniaturize this greenhouse technology and get it up into space, where astronauts can begin to grow their own food on the International Space Station.

CECILIA STANGHELLINI: There are crops that will, not in this future that we can foresee, ever become economic to grow on substrate. Not on Earth, but of course the nice thing about the EDEN-ISS is that money is not an issue, so you can try something without the need to be economic in the sense that a grower would need to be. You know, to bring one kilogram of a payload to the International Space Station costs between 20 and 50,000 euro. It depends on the carrier you are using, but that, that are the prices.

DAN CRANE: Right now, in Antarctica, there’s a crew of botanists and other scientists in isolation at a German research station. Antarctica is like space in a lot of ways — not least because international treaties make it illegal to dump waste. Just like in space, you’re forced to be ingenious about recycling and reusing everything, maximizing your food production.

For ten months, these earthonauts are going to grow salad greens and sweet peppers and other vegetables, while scientists at Wageningen watch and offer advice via video feeds. They’re like little Matt Damons out there. Now, there are good reasons for trying to grow food in space — just ask any soldier how grim it can be to have to live off processed meal rations while on a long, isolated deployment. Growing your own food isn’t just healthy, either. It’s a way to stay in touch with nature, to give astronauts the psychological joy of nurturing life, even when in the cold deadness of space.

CECILIA STANGHELLINI: This specific project is about production of fresh food vegetables, not particularly with respect to, how you say, the diet, because of course vegetables are no calorie, no proteins, but more for the feeling and some quality aspects, and how it contributes to their wellbeing, the idea to have fresh food and also to produce it by themselves.

DAN CRANE: And then this research, again, gets used back here on Earth. For example: Wageningen regularly hold “autonomous greenhouse” hackathons, where people come up with ways of making food as productively as possible with as little human intervention as possible. That means using AI assessing the state of crops visually, and then using robots to pick the crops, for example. The future of agriculture could well be a sea of greenhouse after greenhouse, as far as the eye can see. Each one as safe, streamlined, and hermetically-sealed as life on-board a spaceship.

This isn’t a sterile vision, though. There will be soil in so many of these greenhouses, because soil is still the best and easiest way to grow the caloric crops that keep us alive — as we heard, you’d be a fool to try and grow staple crops like wheat in an underground farm using hydroponics, let alone on the International Space Station. So the answer to those questions from the start of this episode, whether we can go beyond soil, and whether we should even try, is: Yeah, probably, but not entirely.

Throughout this series, we’ve dug deep — ah, there’s a soil pun again, I still got it — sorry — we’ve dug deep into the ways in which we humans have relationships with soil. You can look to the Dust Bowl, and desertification of the Sahel, and talk about exploiting the land. Over-farming, over-grazing, thinking of soil as this resource that we can use without consequence. Seeds go in, food comes out, and that’s all there is to it.

But a future where we grow food intensively in controlled greenhouses could also be the thing that saves soil from human influence, because it would concentrate agriculture in a small number of places. Imagine the rural parts of the world, the farmland near where you live, left to fallow and return to some kind of nature. Going beyond soil doesn’t mean forgetting its purpose or its presence, but it could mean releasing it from our control.

Soil is part of the mutualistic ecosystem of the planet. There’s the life in soil, microbes and worms — dancing or otherwise — that have direct influence on our lives. It can make us sick, or be a source of miracle antibiotics. Soil is a dark universe that we barely understand. We’re exploring it now, but it’s still early days. There’s a lot left to understand, and to appreciate.

In the mid-20th century, the phrase “Spaceship Earth” became a popular rallying cry for environmental and social justice. As U.S. politician Adlai Stevenson said, in a speech to the UN in 1965:

ADLAI STEVENSON: We travel together, passengers on a little space ship, dependent on its vulnerable reserve of air and soil; all committed for our safety to its security and peace; preserved from annihilation only by the care, the work, and, I will say, the love that we give to our fragile craft.

DAN CRANE: I hope this show has made a convincing case for a new twist on that old idea. We’re all living in Greenhouse Earth now. But maybe the greatest thing that could come from moving beyond soil is to finally break that link between soil and exploitation. Making soil an extra, an option, on a smorgasbord of options for feeding the world. We can let it be dirt again, let it be what it wants and needs to be.

The climate is changing, people need food. Things aren’t perfect. But the floor of Greenhouse Earth is dirty. That dirt is ready to help just as soon as we stop, look down, and listen to what it can offer us.