Carl Zimmer explores the hidden world of the aerobiome

If you’re lucky enough to live in a place with decent air quality, the surrounding medium might seem like empty space — a nothingness that deserves little attention beyond how hot or cold it feels. 

Carl Zimmer might change your mind about that. In his new book, Air-Borne, the celebrated science writer — who pens The New York Times “Origins” column and has authored 15 books over a 35-year career — tells the stories of the invisible organisms that inhabit our atmosphere and the intrepid scientists who discovered their existence.

As you read, you’ll fly with aerobiologists who risked asphyxiation to scour the stratosphere for floating life. You’ll serve as Dr. Watson to scientific Sherlocks investigating the microscopic purveyors of terrifying diseases, from tuberculosis to COVID-19. You’ll root for the researchers who sounded the alarm about airborne diseases yet were repeatedly and wrongly rebuffed. Above all, you’ll gain a new appreciation for each and every breath you take.

The air, Zimmer writes, is “a gaseous ocean in which we all live, which infiltrates our bodies, which our own bodies transform and then return to the great transparent sea….” In this interview with Zimmer, Big Think dives right in.

The following interview has been edited for length and clarity.

Big Think: Louis Pasteur takes a central role in your book. How much credit do you think he deserves for producing the far less deadly world we live in today?

Zimmer: Pasteur did so much that it’s easy to forget some of it. One of his earlier efforts was to destroy “spontaneous generation” — the idea, which lasted for centuries, that life could be spontaneously produced from decaying matter. By the mid-1800s, people knew a dead rat didn’t spontaneously produce maggots. Flies would lay eggs on them. But microbes were still a matter of debate. 

So, when Pasteur was looking at fermentation, how alcohol was produced, and how those batches could spoil, he decided the best explanation was that germs are floating in the air. If they happened to land in a vat, they could spoil it. No spontaneous generation needed. 

This [explanation] was controversial at the time. Pasteur got into a very public debate trying to persuade people that we’re surrounded by floating germs. A French journalist declared that he was attempting to bring us into a world that was too fantastic to believe, and Pasteur did some fantastic things to prove it. He climbed a glacier. He went all over France with these big flasks to collect bacteria from the air. 

Certainly, Pasteur is hugely important to modern public health. He has helped to save many millions of lives. He was also an aerobiologist. That part of his life and work has been forgotten.

Big Think: I loved your description of the aerobiologists. They were pushing the limits, not just to see how high they could go. They were looking for life. How did they push their field forward?

Zimmer: The modern age of aerobiology happened with the invention of airplanes. I write in the book about Fred Meier, a plant pathologist who hopped in airplanes to find out about these diseases that are wiping out wheat fields and other crops. He would go up and wave these Petri dishes on handles out of open cockpits. The pilots thought he was crazy, but he would actually collect stuff. He once collected fungi from 18,000 feet over Washington, D.C. 

But Meier kept pushing and pushing. When he found out that Charles and Ann Lindbergh were going to fly over the Atlantic, he talked them into helping him, and they found life over Greenland, which was amazing. He partnered with adventurers going up into the stratosphere with a giant balloon. They took along his equipment, and lo and behold, they showed that fungal spores could survive in the stratosphere despite the incredibly toxic conditions. They found that out in the mid-1930s. It blew peoples’ collective minds that life could get that high.

Big Think: There is a passage in your book where you described how hostile Earth’s upper atmosphere is, and yet there’s life up there! [However], I don’t notice much talk about looking for life in other planets’ atmospheres.

Zimmer: You’re absolutely right that the real focus of astrobiologists right now is either digging into the soil of Mars or drilling into one of these ice-covered moons in the outer solar system. There’s good scientific justification for going to those places. Who knows what we’ll find? 

But a small group of scientists would like us to think about Venus. You won’t find anything on the surface of Venus because you can melt lead there, but it’s not so bad in the clouds. 

We know that on Earth there are bacteria, lichen, all sorts of things in clouds. When you look at a cloud, you’re looking at a living thing. Trillions of organisms [representing] thousands of species are in each one. They’re alive and, in some cases, are growing because they’re eating the cloud. 

So, these scientists have said, “Maybe life arose on Venus’ surface, and it got into the atmosphere. Then maybe, just maybe, some of it survived there — cycling up and down through the layers of the atmosphere.” It’s a tantalizing idea, and it wouldn’t be that hard to test. Just shoot a probe through some of these clouds, and you should get a pretty good idea.

Big Think: Much of your book is about scientists stubbornly refusing to accept that diseases could be airborne, even into the mid-20th century. What were their motives here?

Zimmer: Infectious disease scientists [and] public health authorities saw an incredible shift in the understanding of diseases in the late 1800s. Before then, prominent medical authorities assured everyone that most infectious diseases were actually not infectious. They were caused by miasmas, disturbances of the air. Somehow, the air became corrupted, and if you inhaled it, you might get malaria, influenza, cholera, and on and on. 

Then the architects of the germ theory of disease worked long and hard to demonstrate disease by disease that they were actually caused by pathogens. Those pathogens, as they were identified, were not in the air. Cholera is caused by bacteria, and that bacteria is in water. Yellow fever is caused by a virus that’s in a mosquito. Syphilis is caused by a bacteria that’s spread through sex. So you have food-borne diseases, waterborne diseases, sexually transmitted diseases, and so on. These scientists were pulling diseases one by one out of the air. 

That led to the view that the air was basically harmless, and it would take a lot of evidence to persuade them otherwise. You have to wonder if they were ever going to be persuaded because they have taken this consensus as almost a law. Generations of medical students and public health experts were trained this way, and it’s still a widespread view.

Big Think: Fast forward to modern times: Why do you think many public health officials and scientists hesitated to declare COVID-19 airborne even into late 2021?

Zimmer: We were dealing with a new disease when the COVID pandemic hit. Scientists were trying to gather data on this disease to understand what we were dealing with. At the same time, they were also falling back on older paradigms. 

A default assumption was that this is a respiratory disease, so it’s probably spread by large, heavy droplets. But a few experts said, “This looks like it might be spreading like smoke in a room.” In other words, this is airborne. There was a lot of pushback against that — partly because many people didn’t understand the science of airborne disease as we understood it in 2020 already and partly because they were waiting for evidence. 

It did take time for a whole series of case studies to be published, for there to be outbreaks, and for scientists to figure out what made the most sense for how the virus spread. Finally, there was a consensus that COVID-19 is airborne.

Big Think: Between SARS, H1N1, and COVID-19, humanity has already faced three deadly bouts of infectious disease this century. How prepared are we for another when it inevitably arises?

Zimmer: We’re in a better position than we were before the SARS epidemic in 2003. You have to remember, in the early 2000s, the idea of entirely new diseases emerging and sweeping the planet was still unfamiliar. We understand the basics better. One way to prepare is to stockpile stuff that you may need and to make sure those stockpiles are still working. Developing better technologies for vaccines is important. Testing is important, too. Governments have made investments in all those things, but whether they’ve done enough is an open question. 

At the start of the COVID-19 pandemic, the United States had those stockpiles, but they were largely emptied out already. A lot of the stuff that hospitals were holding on to were old and decrepit. The rubber bands would literally snap off [masks]. Things were in a bad situation because we recognized the importance of stockpiles but we didn’t follow through. 

We now have Nobel-Prize-winning mRNA vaccines that can be made quickly. [However], in the United States, we have state legislators who want to ban mRNA vaccines altogether based on claims that have no scientific basis.

So, you can have all these great developments, but if you don’t use them in the right way, if you’re not organized, the next pandemic could just roll over us.

Big Think: What are the risks of a catastrophic outbreak in our staple crops? What steps are scientists and farmers taking to prevent them?

Zimmer: Diseases from the skies have been the bane of farmers’ existence for thousands of years. In the Bible, when God threatens to smite humanity, he will talk about things like stem rust. Of course, the Bible is not presenting these things as living organisms, but that’s what they are. Even as countries like the United States dramatically expanded their farm production in the 1800s and 1900s, they could never permanently escape these ancient diseases. 

In a way, we made it easier for airborne diseases because farmers often use the same variety [of crop] because it can resist the pathogen. If you have wheat that can resist black stem rust, then everybody plants it. Well, that stem rust evolves quickly, and there’s a good chance that a new stem rust variety will evolve that can attack the farms again. 

Right now, a bad stem rust is causing a lot of trouble in Africa. It has spread by the wind into Asia and is moving from country to country. Scientists have been trying to develop computer programs to try to predict where this stem rust will go next. It could eventually make it to the United States. We have been spared these huge stem rust outbreaks, but they could very well come back. 

Big Think: How have humans transformed the “aerobiome” in the last 50 years, and what are some of the ramifications?

Zimmer: The aerobiome is basically all the life in the air. Just like we have a microbiome inside our bodies — which is made up of thousands of different species — there are many, many more species floating around us. The aerobiome has existed pretty much since life began. When life emerged, cells would have been floating around on the ocean’s surface, and when there was a wave that crashed, tiny droplets would fly up into the air and take life with it. So the aerobiome is very old, but we humans have changed the planet in all sorts of ways, and one way is by changing the aerobiome itself.

For example, the kinds of microbes that live on huge industrial farms are different from what would have lived on the prairies that were there before. If you bring a bunch of pigs together on a gigantic farm, they will share viruses like foot-and-mouth disease, and those viruses will create airborne plumes that will travel for 40 miles or more. We have produced lots of antibiotic resistance here on ground level because we prescribe a lot to ourselves. 

We also feed farm animals huge amounts of antibiotics, so bacteria have evolved lots of resistance. Those bacteria then go up into the air. Those clouds will drift along, and they will rain down bacteria with those resistance genes. Trillions rain down every year. 

And we’re continuing to change the aerobiome with climate change. That changes the formula with the winners and losers in terms of who will get into the air and survive.

Big Think: I love your description of air “as a gaseous ocean in which we all live.” Did researching and writing the book change how you live within this ocean?

Zimmer: It has changed how I think about things. I take masks with me to be on the safe side. If I’m at a place where there are vulnerable people, I put on a mask in case I have something that I don’t know about. I don’t want to endanger them. So I am more mindful of how things in the air can make me sick.

At the same time, I have become keenly aware that I am probably breathing in thousands of living things with each breath. For the most part, I’m fine. It makes me more interested in research people are doing about the positive experiences we are having with the aerobiome. Maybe it’s good for us to have these living things floating around in our airways — sampling them, breathing them in and out. It may help to train our immune system. Some small studies on animals suggest they might even affect our mood. There’s a whole area of research about the aerobiome that has yet to be done.