Instant Genius - The hidden life in the air we breathe

Episode Date: July 20, 2025

Every day we all breathe in thousands of litres of air, it is, of course essential for our continued existence. But did you know that the air that surrounds us is filled with a thriving colony of life itself? This is known as the aerobiome – a population of thousands of species of bacteria, fungi and even potentially lethal viruses such as SARS-CoV-2. In this episode, we speak to science journalist and author Carl Zimmer about his latest book Air-Borne – The Hidden History of the Life We Breathe. He runs us through the fascinating history of aerobiology, outlines the key role the field played in developing the germ theory of disease, and explains how even clouds are filled with life. To get the exclusive gift box from Shokz, order via this link: ⁠https://bit.ly/4kFt10l⁠ Learn more about your ad choices. Visit podcastchoices.com/adchoices

It's peak pollination season, and my business is scaling fast. To keep the nectar flowing, I need a phone plan with top priority data speed. That's why I chose Google Fi Wireless. My connections stay strong even when the hive is buzzing. Plus, unlimited plans start at $35 a month. Now that's a deal that doesn't stay. Explore Google Fi Wireless plans today. Plus taxes and government fees.

Google Fi Wireless is not subject to data traffic deprioritization during times of high network usage. You said this place was steps from the water. We just haven't found the steps yet. How much did we save? Enough. Enough to get lost. Or you could book a stay with Hilton. Welcome to your oceanfront room.

Just steps from the water. The Hilton sale is on now. Book on Hilton.com or the Hilton app and save up to 20% to get the stay you expected. When you want savings, not surprises. It matters where you stay. Hilton for the stay. No one goes to Hank's for his spreadsheets.

They go for a darn good pizza. Lately, though, the shop's been quiet. So Hank decides to bring back the $1 slice. He asks Copilot in Microsoft Excel to look at his sales and costs. Help him see if he can afford it. Co-pilot shows Hank where the money's going and which little extras make the dollar slice work. Now, Hanks has a line out the door.

Hank makes the pizza. Co-Pilot handles the spreadsheets. Learn more at M365Copilot.com slash work. This podcast is sponsored by name, audio and focal. Streaming has made music more accessible than ever, but true listening is about more than ease. It's about quality. British audio experts name audio,

alongside French acoustic specialist focal, combine handcrafted tradition with cutting-edge innovation and high-end materials, delivering digital precision with analogue warmth. So you can experience exceptional sound at home. Music just as the artist intended. Visit name audio.com to learn more. Hello and welcome to Instant Genius, a biotized masterclass in podcast form.

Every Monday and Friday, you'll hear world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Jason Goodyear, commissioning editor at BBC Science Focus. Every day we all breathe in thousands of litres of air. It is, of course, essential for our continued existence. But did you know that the air that surrounds us is filled with a third, thriving colony of life itself. This is known as the Aerobiome, a population of thousands of species of bacteria, fungi, and even

potentially lethal viruses such as SARS-COV-2. In this episode, we speak to science journalist and author Carl Zimmer about his latest book, Airborne, The Hidden History of the Life We Breathe. He runs us through the fascinating history of aerobiology, outlines the key role the field played in developing the germ theory of disease, and explains how even clouds are filled with life. So welcome to the podcast. Thanks very much for joining us. Thanks so much for having me. So today we're talking about your book, Airborne, the hidden history of the life we breathe. So I have to ask the obvious question first. Were you motivated to look into this

topic due to the COVID pandemic? That's certainly where the seed was planted. I was working as a journalist writing for the New York Times. And my colleagues and I, we were all reporting on this new virus and how scientists were trying to understand it as fast as they could. And one of the debates that really took me by surprise was how it spreads. So a lot of us, certainly I was wiping down my groceries at the beginning of the COVID pandemic. And then there was this big debate where some people were saying, no, actually, COVID is airborne. In other words, it's kind of like smoke that someone might be puffing out from a cigarette. Wiping down your groceries is not going to protect you.

And that got me fascinated. Like, why was that a debate? Why was that so hard to sort out? Because that, you know, the World Health Organization initially said, COVID is not airborne. And about two years later, they finally said, in print, clearly, yes, it is spread through this long-range airborne transmission. It fascinated me.

And when I would talk to scientists, they'd say, well, this is part of a history. And you have to understand the history, the bigger context to understand what we've just gone through. And what I came to appreciate is that there's been a long history of scientists struggling to understand what's in the air, what living things are around us, what are we breathing in. And, you know, we still don't really have a very good handle on it. We're still discovering what science is called the aerobiom. It's arguably the least understood

realm of life on Earth. And so from that seed in the pandemic, it really like bloomed into this much bigger study, for me, an exploration of this living atmosphere that we live in. Yeah, so we learn at school that air is mostly sort of 78% nitrogen, about 20, 21% oxygen. But we now know that it's full of other bits and pieces. And what's fascinating about this from reading your book is something we haven't really known that long. So if you take, for example, quantum physics, it's about 100 years old, and it seems like a wild theory. But we've only just started figuring out these airborne particulates and pathogens, etc. In about the same time frame, I think that's pretty wild.

I agree. I agree. In the 1800s, you know, when people started to broach this basic concept, people thought they were crazy. I mean, I'm talking about like Louis Pasteur. You know, Louis Pasteur actually became convinced around 1860 that we are surrounded by what he called floating germs. And people said, no way, this can't be right. And it wasn't until the 1930s that this science of life in the age, Air got a name, aerobiology. And so it really is a testament to how tricky and elusive this living atmosphere is. I mean, we are surrounded by so many floating cells and other forms of life. But for the most part, they're invisible. They're spread out across this, you know, vast

atmosphere all the way up to the stratosphere. So it's very hard to, study them. And yet, as we saw on the pandemic, they can turn our existence upside down. So let's go back a little bit deeper into history. So you talk about, so we'll go on to the germ theory of disease in a moment. But going further back, we had this idea of the myasma. So what does that mean and what was the concept? So this is a concept that arose in ancient Greece. originally the word referred to a sort of a curse, a stain that people might suffer for some moral crime, and it had to be expiated, you had to be purged of it. And so this may have been like an explanation for why it was that, you know, farmers might suffer a terrible crop failure,

or why a city might be hit by a terrible plague, that they were being punished. Hippocrates and his followers, they transform myasma into a more natural thing. They argued that the air itself could become corrupted. And if you breathe in that corrupted air, that could cause you a disease. And so different diseases were thought to have different kinds of myasma. And different species could inhale different kinds of miasmas to cause different diseases. it's not actually like what we think of today as, you know, infectious diseases spreading through the air because they just didn't have a concept of bacteria and viruses and so on. It was somehow the air itself

became corrupted. And, you know, like people, you can sort of imagine, you know, people would be walking around and not really knowing what the atmosphere is around them, but, you know, some days it would smell weird or it might just become strangely humid and, you know, the air has these strange qualities. And so people would say, like, oh, you know, there might be a myasma here. And this concept sticks. It lasts in one form or another for centuries, you know, past ancient Greece into Rome. And then when Europeans rediscover, you know, the classical writers, they take up miasmas as well. And so even in the, you know, the 1800s, when cholera hits England, for example, for the first time, what's the explanation that it's some sort of corrupted air. Maybe there's waste on the ground or the rivers

are too sluggish, and so somehow the air is being poisoned and people are inhaling bad air and getting cholera. Completely wrong, but this was what all the experts were maintaining in the 19th century. So let's jump forward then, because obviously we had a sense if there's some sort of way that the air can infect us. But then we move forward to the germ theory of disease, which we take for granted now. But that wasn't always the case. A lot of scientists, prominent scientists, were very resistant to the idea. Yeah, I think people assume that when, you know, some scientists get an idea that in hindsight we know is right, we just assume that everybody said, oh, right, okay, got it, good. And then we almost,

move on and, you know, science moves forward in a straight line of progress. And it just isn't how the history of science has worked, especially in medicine and biology. So, you know, these microorganisms, this microbial world of bacteria and viruses and so on was discovered in the 1600s with the invention of microscopes. And by the 1700s, there were people who were arguing that all sorts of diseases like tuberculosis or plague and so on were caused. by these microorganisms. And they were laughed at. They were nicknamed the contagionists because they had this idea that these microorganisms were going from one person to another as opposed to, you know,

a myasma, which are just waft along and like, you know, poison gas could just hit a bunch of people at once. So we're talking, you know, about two centuries of fighting about what caused these diseases. And it really wasn't until the late 1800s that these contagionists really kind of lined up all the evidence that they needed, the experiments and also sort of the concepts to really lock it in, to be able to sort of like, hey, I can show you that this one species of microbe, you know, say mycobacterium tuberculosis, causes a particular disease, tuberculosis, and they would do animal experiments and so on to drive that point home. So it took this incredibly long time before the miasma concept collapsed. And when it collapsed, it collapsed very quickly. So I guess we should ask, how are these pathogens carried in the air? Like we mentioned earlier, like this sort of crude composition of the air that we breathe. But how are the pathogens actually spread in the air?

How do they sort of latch on? Well, I mean, an important thing to note is that, in fact, you know, many pathogens. pathogens don't spread through the air. And this is actually one of these initial insights from the germ theory of disease, which is that, you know, cholera is spread by bacteria in water. Typhoid is spread by other pathogens in water. There are some, you know, malaria or yellow fever are spread by mosquitoes. Others are spread by lice or by fleas. So really, the germ theory of disease proponents, they couldn't understand how anything could spread through the air, honestly. they didn't see any evidence for it. Now we know that now that that's not true, and that's thanks

in large part to some important work that was done in the mid-1900s. So the basic way that a disease like COVID or tuberculosis or measles or these other airborne diseases spread is that they're infecting our airway. So that means that these viruses or these bacteria or what have you, they're going into cells and they're making copies of themselves and they're coming out and they're finding a new cell to infect. And we're breathing. And every time you breathe in and then breathe out, you are actually like generating lots of tiny droplets, invisible droplets. I'm not talking about spitting. I'm just talking about breathing. And these tiny droplets come out of your mouth and nose and then they float away. Some of them will drop within a few feet, but a fair

number of them will just keep on floating. They defy gravity. And inside some of them are viruses or bacteria or fungi, what have you. And so if other people are in the area, like in a poorly ventilated room, they can inhale them. And those organisms can find themselves in a new home. And you have an infection that is then spreading. When you need to build up your team to handle the growing chaos at work, use Indeed, It gives your job post the boost it needs to be seen and helps reach people with the right skills, certifications, and more. Spend less time searching and more time actually interviewing candidates who check all your boxes. Listeners of this show will get a $75 sponsored job credit at Indeed.com slash podcast.

That's Indeed.com slash podcast. Terms and conditions apply. Need a hiring hero? This is a job for Indeed sponsored jobs. Wishing you could be there live for the big game. Soaking up the atmosphere and the crowd, but too often, life gets busy, or the price holds you back. Priceline is here to help you make it happen. With millions of deals on flights, hotels, and rental cars, you can go see the game live. Don't just dream about the trip. Book it with Priceline.

Download the Priceline app or visitpriceline.com. Actual prices may vary, limited time offer. This podcast is sponsored by name, audio, and frocule. With over 100 years of combined expertise, Name and Focal have been bringing music to listeners just as the artist intended. Since day one, this mantra has shaped every innovation in high-fi design, technology and acoustic engineering, balancing craftsmanship and tradition with pioneering thinking. Name Audio pushes cutting-edge technology to ensure digital precision whilst sustaining Pratt, pace, rhythm and timing. The elusive quality that

makes music feel alive and gives it emotional texture. Today, in partnership with French acoustic specialist focal, name audio creates systems that deliver exceptional sound and unforgettable listening experiences at home. Try it for yourself at a focal powered by name boutique. Visit focal powered by name.com for more information. So let's have a look at sort of prevention of this then. So during COVID in the UK,

we were told to all wear masks. And interestingly enough, no one does anymore, but 20 years ago, I spent several years living in Japan. And they always wear masks even if they get a common cold. You know, it seems to be out of politeness or manners or something like that. That's right. But is that an effective measure to take? You know, should we still be doing it, really, is why I'm asking?

Well, I would say that to answer that question, you have to look at the context. So, you know, when we are facing a new global pandemic and there are no vaccines available for months to come and all we can do is try to slow down the spread, then that makes wearing masks really, really valuable because, you know, masks, you know, do reduce transmission. How much transmission it stops depends. You know, are you just using a piece of cloth? Are you using an N95 respirator, which can just stop lots and lots of droplets from getting out of your mouth or getting into your out. So yes. So in those situations, it's very important. And then, you know, we have to sort of make, make these sort of, you know, individual and public health decisions about other times. And that can

depend on, you know, sort of some cultural views on these things. You mentioned Japan throughout East Asia for decades. Masking has not felt like some strange alien imposition. It's just what you do. if you're sick, you want to, like, do people a favor so that you're not, like, just exhaling viruses on them because, yes, cold viruses are airborne. Influenza appears to be, at least in part, airborne, and so on. Like, common diseases are also airborne. So, you know, we do need to think about that, I would argue, in Western societies as well. You know, we live together and we breathe the same air. Whether you like it or not, You are breathing in with somebody else exhaled, especially if you're in, you know, a train car or in a classroom with no windows. You're all breathing the same air.

So sticking with that, so a few years back, I actually did get COVID. And I sort of quarantined myself in the spare room. I was wearing a mask whenever I walked around, washing my hands, everything, all the windows open. My wife still got it. So are there any measures we can take in the home that can help prevent this sort of thing? Should it be built in our architecture, for example? There are certainly different layers of protection that we can put in place, especially when we're dealing with a pandemic.

Now, they're not a guarantee that the virus is not going to be able to hop from one person to an X. You know, airborne pathogens can be really good at getting around from person to person, partly because, you know, every time you're exhaling, you may be exhaling those COVID viruses, and we all have to breathe. So we're sampling the air, you know, every few seconds, 24 hours a day. So that is why COVID was able to spread so fast. And what you did opening the windows, that's really great. You know, it's good that, you know, it was warm, enough that you were able to do that, you know, a person who is sick wearing a mask and isolating from other people, that that is also very helpful. Are there other things that can be done? Sure,

there are things that, you know, there are air purifiers, filters for, you know, ventilation systems, which are really good at stopping particles and including, you know, droplets that might carry viruses. And those, you know, you can think of as more layers that will reduce the chances of infection. And, you know, it may be that there may be still more kinds of technology that might become commonplace in the future. So, for example, you know, how well ventilated is your house? I mean, do you know? There's a pretty simple way to find out is to get a carbon dioxide meter. I own one. But, you know, you have to go out and get it. it and figure out how it works and all the rest. But, you know, we're starting to see carbon dioxide

concentrations being displayed on thermostats. So a room will show you, well, what's the temperature in here and how high is the carbon dioxide level? If it's a high concentration, that's telling you that there are a lot of people in there and the ventilation is not good, that's a place to be concerned about, especially if there's an outbreak of influenza or some other disease in your community. Is that just because we're breathing out carbon dioxide? Yeah, so carbon dioxide, exactly, is what we exhale in high concentrations. And so if you sit by yourself in a room that has very little ventilation and you look at a carbon dioxide meter, you close a window, you know, you seal it off, you can see the carbon dioxide level go up. And that's your carbon dioxide.

In other words, the air is becoming more and more just your exhalations. And so whatever else you're exhaling is going to be floating around in the room as well. Now, if you have like four or five people in that room, karma dioxide level is going to go much faster. And on the other hand, like if you have a good ventilation system in place or you're able to open the windows, you can see the carbon dioxide level go down and stay down. And so that's a, you know, that's a good proxy. It's a good rough and ready measure of ventilation and risk of infection.

So another thing that I've heard people talk about is ultraviolet light. So, you know, what role does that have to play in this? So back in the 1930s, in the sort of the golden age of aerobiology, a team, a husband and wife team named William and Mildred Wells, discovered how droplets can carry viruses and bacteria around. And then they said, well, how can we stop it? How can we purify the air? And they played around with different things.

And eventually they discovered that ultraviolet light is really effective. And so in 1940, in a measles epidemic in Philadelphia, they had actually installed ultraviolet lamps in some classrooms in a school. And the kids in those classrooms are 10. times less likely to get measles than other kids in the same school. And so that was the first really strong demonstration that ultraviolet light can potentially really help in reducing transmission. So today, there are, as airborne disease has been rediscovered, there's been a resurgence of interest in ultraviolet lights that people could install, particularly in public places.

You know, places where a lot of people come together and, you know, great places for transmitting diseases. Schools, movie theaters, train stations, places like that. And these are very small and they're more effective than what was used in the 1930s because it's a particular frequency of ultraviolet light that's just really good at being able to essentially kind of sweep across a large swath of the air and kill off. viruses and bacteria that are floating around, but also not be harmful to us in terms of, you know, hitting our skin and, you know, maybe causing cancer, something like that. They, they don't run that risk. So, yeah, so ultraviolet light is a, is a very exciting area. There's still a lot of work that has yet to be done, which means that, you know, as we think about future pandemics, doing research on these new kinds of technology is really important.

because we know what happened in COVID. And anything we can do to reduce that toll is going to be for the better. Great. So let's shift gears a little bit then. Something else you talk about in the book, something that I suffer from, I mean, pretty badly, to be honest, is hay fever. This fascinated me that even this took a great deal of work to figure out what was going on. Yeah.

I mean, I think anybody who gets hay fever feels like everything is incredibly obvious about this condition that can be so tormenting. But, you know, the fact is that even in the 1800s, the very basics of it were unknown. A lot of experts were convinced that what we would call hay fever allergies, they must be some kind of infection. and it was actually the work of a British physician, Charles Blackley, that demonstrated initially in the mid-1800s that it was pollen. He would walk by a field of hay, and suddenly he would get hit by this hay fever, which he hated. He was tormented by really bad hay fever his whole life. And he thought, huh, well, I know that plants release pollen.

so maybe it's the pollen that's causing this for me. And so he would actually then do experiments where you would get, he would have some flowers in his house, and he would kind of rub the pollen on his fingers and put in his nose, and he would instantly have a horrible reaction to it. And, you know, honestly, like, I mean, at the time when he published his results, most people just didn't believe him. Some people actually thought the hay fever was what they described as a neurosis.

they just could not understand, like, this just seems so weird. I mean, why would pollen cause these symptoms? It doesn't make sense. And really, it wasn't until the 20th century that the whole concept of allergy, you know, of harmless substances triggering strong, really unpleasant immune responses, really emerged. So, yeah, so he was way ahead of his time. And he was ahead of his time in another way.

he asked himself, okay, this pollen that I am inhaling and is making me miserable, where is it coming from? Okay, is it just coming from the, you know, the farm next door? So he got this great idea to fly a kite, to catch pollen. He wondered, how high can I fly my kite and catch pollen grains? He had this little sort of sticky tape that he put on the kite. And this is the first time really anyone had done anything like this. It was just incredibly brilliant. And he would fly his kite up over a thousand feet in the air and he would catch pollen grains. And so he thought to himself, oh my goodness, there are these high altitude rivers of air that are carrying along pollen in incredible distances. He would go to the beach and fly his kite when the wind was coming in from the ocean. And there again,

he would be catching pollen grains. And he'd say, well, clearly these pollen grains have traveled incredible distances across vast stretches of water. And so this is one of these early insights into what aerobiologists know today, which is that indeed life can go up into the air, can go actually maybe 20, 30, 40 miles into the air, and then can travel across the planet hundreds or even thousands of miles. So let's stick with that then and talk about clouds. So most people think clouds are just made of of water or you might hear the strange stories about raining frogs or whatever, things like that. But there's a lot more going on there, isn't there? Yes, every time you look at a cloud, you're looking at a living ecosystem.

You're looking at a cloud of life, thousands of species, perhaps trillions of individuals, a lot of bacteria, some viruses, there might be lichen up there, there might be fungi up there. they've been swept up from the ground, from the ocean, off the surfaces of trees, their leaves and their bark, and they have gone up and some of them ended up in clouds. And when they're in those clouds, it's really kind of, they're like mysterious islands that's very hard to visit. So biologists don't really understand what's happening inside of them. One way that you can get clues is to build, you know, weather stations up on the top of mountains where, you know, low-hanging clouds can float by and then sample the clouds as they pass along. And it looks as if the bacteria, at least, in these clouds, some of them seem to be able to

feed on organic compounds that are in those tiny droplets in the clouds. So they're actually, they're eating the clouds. and they're growing, albeit very slowly, but they are growing because they can have a metabolism up there. It's a very difficult, challenging environment to be in, but some microbes are tough enough to handle it. And what's particularly fascinating is that living things in clouds are really good at drawing water molecules around them that can then form into bigger droplets, or crystals, which can then fall. So in other words, life can seed rain from clouds. So when it's raining, you can have the aerobiome in part to thank for that.

And some of those raindrops are going to contain living things. Rain is not sterile. It's got lots of life in it. So we've talked about an awful lot there, really fascinating stuff, all of it. So you talk about aerobiology. So what are some of the big questions that are remaining that scientists really want to uncover? Yeah, aerobiology is mostly big questions. It started in the 1930s.

It had a slow start, and then it really got sidetracked because of war. Biological warfare became this enterprise that attracted thousands and thousands of aerobiologists. can we make bombs that can spread pathogens through the air? So can we, you know, instead of trying to protect people from airborne disease, can we use airborne disease as a weapon? And in Britain, in the United States, in the Soviet Union, and some other countries, this was a huge undertaking. That doesn't really tell you much about the natural world of the aeroboom. And so, you know, we're wondering, well, how high can life really go? It's still not clear. We don't have, have kind of a global picture of how life travels around the world. You know, you can think about these

big weather maps that we have. These are global weather maps showing how fronts move around and clouds move around. These are magnificent things. And we could potentially have a biological version of that, you know, to see the, the aerobiooms spurting around the world as a unified system. But we don't have that yet. And that's really important for a lot of reasons, because both for human diseases and diseases that can destroy, you know, a country's food supply, we really need to know where some of these pathogens are traveling over long distances. You know, there are fungi called rust that can destroy wheat or coffee or other big crops, and they do not respect national boundaries.

You know, the spores go up in huge numbers, and then they get carried along by the wind. And, you know, some of these species of rust have been documented going from country to country. And, you know, the question is, well, how far are they going to go? You know, does a rust that is starting in, say, Uganda, will it get to the United States? We can't say that. So huge, big questions are left to be answered. Thank you for listening to this episode of Instant Genius.

from the team behind BBC Science Focus. That was Carl Zimmer. To discover more about the topics we've just discussed, check out his book, Airborne, The Hidden History of the Life We Breathe. If you liked what you just heard, then please do consider subscribing to Incident Genius on your preferred podcast platform.

If you'd like to see our guests and hosts in person, then please also check out our YouTube channel, at Science Focus. The current issue of BBC Science Focus magazine is out now. Pick up a copy wherever you buy your favourite magazines, or download us on your app store of choice. You can also find us on Apple News or online at sciencefocus.com. This podcast is sponsored by Name, Audio and Focal.

The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analog warmth. Alongside French acoustic specialist focal, name creates high-end audio systems, combining innovation with craftsmanship, So you can listen to music, just as the artist intended. Discover more at name audio.com. Ambition comes in all shapes and sizes. At First Citizens Bank, we roll with your goals,

because we're built for what you're building. Fit for your ambition for Citizens Bank. Enjoy more ways to save at Ralph's, like low prices in every aisle. And when you download the Ralph's app, you can clip and save more with digital coupons every week. Plus, you can earn fuel points to save up to $1 per gallon at the pump. At Ralph's, you can enjoy more ways to save and more rewards every time you shop.

So it's always easy to save big every day with savings and rewards. Ralph's SoCal for over 150 years. Savings may vary by state. Fuel restrictions apply. See site for details.