The Alchemy Of Air

23:46 minutes

A bust of Julius Caesar. Credit: Shutterstock

Did you know that’s it’s not only possible, but probable, that for every breath you take, at least one molecule you inhale was expelled by Julius Caesar when he spoke his final words? Sure, that was one gasp, released more than 2,000 years ago. But even though a single exhalation represents just 0.00000000000000000001 percent of all air on earth, it also contains 25 sextillion molecules. When you crunch the numbers, it turns out that roughly one particle of air exhaled not only by Caesar, but also Cleopatra, Alexander the Great, and George Washington, will make it into your next breath.

The air we breathe is tied to history, and not just human history, but also Earth’s geologic past. Science writer Sam Kean joins Ira to discuss the fascinating story of these gases in his new book, “Caesar’s Last Breath: Decoding the Secrets of the Air Around Us.”

[Could there be an Earthly origin for moon oxygen?]

Segment Guests

Sam Kean

Sam Kean is a science writer. He’s the author of The Bastard Brigade and Caesar’s Last Breath. He’s based in Washington, D.C.

Segment Transcript

IRA FLATOW: Next up, take a deep breath.


Mm. It’s not only possible but probable that one of the molecules that you just inhaled was expelled by Julius Caesar when he spoke his final words, “Et tu, Brute?” Now, I’m not making this stuff up. I know what you’re going to say, it’s just one breath expelled over 2,000 years ago. How could I be inhaling those same air particles? There’s no possible way there should be anything left.

But as you’ll soon hear, the math that we’re talking about does check out. And that’s because many of the molecules that make up our air, like nitrogen, are surprisingly hardy. They stick around for hundreds, even thousands of years, which means every breath we take is in some way tied to Caesar or Cleopatra, Alexander the Great, George Washington, Kim Kardashian. The air we breathe ties us to the past. And not just the human past, but Earth’s geological history, as well.

And the story of these gases and our relationships to them is explored in a really good new book, Caesar’s Last Breath Decoding the Secrets of the Air Around Us, by science writer Sam Kean. And he joins me now to talk about it. Welcome back.

SAM KEAN: Hi. Thanks for having me back.

IRA FLATOW: This is a great story. The way you talk about air, I mean, you have a great talent for writing.

SAM KEAN: Oh, well, thank you.

IRA FLATOW: Let’s get the heavy math out of the way first here.

SAM KEAN: All right.

IRA FLATOW: How do we know that, every time I inhale a breath of air, I’m actually bringing in Caesar? Maybe a molecule or something of Caesar’s?

SAM KEAN: Yeah, there’s kind of two forces working against each other here. One is how small an individual breath seems compared to the atmosphere. It seems minuscule. Very, very tiny percentage. It’s something like 19 zeros with a one after them. Very small.

But the other thing is that, every time you do take a breath, you inhale something like 25 sextillion molecules, which is a 25 with 21 zeros after it. So that’s almost incomprehensibly large. And if you do the math, you kind of work through everything, turns out that those two numbers, the really big one and the really small one, almost exactly cancel each other out. And so statistically, it turns out that every time you breathe, there’s a very good chance you’re inhaling probably about one molecule that Julius Caesar exhaled when he died in 44 BC.

IRA FLATOW: And that would be a molecule, then, for everybody in the world.

SAM KEAN: Yeah, everyone in the world.

IRA FLATOW: Who’s ever lived?

SAM KEAN: And there’s lots more left over, because there’s seven billion of us, there’s 25 sextillion molecules. So there’s plenty more.

IRA FLATOW: We can share.


IRA FLATOW: Why does the air last that long?

SAM KEAN: It’s mostly the nitrogen in the air. A lot of the components of the air are reactive. They go away after a while. But nitrogen is a very, very hardy molecule. Sticks around for millions, maybe even billions of years. Two atoms of nitrogen with a triple bond between them, very, very stable, very hardy. So once nitrogen gets in the air, it stays around for a very long time, usually.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from PRI, Public Radio International. Talking with Sam Kean about his new book Caesar’s Last Breath. Let’s go back to the very beginning, because one of the most fascinating parts of the book, because I’m a geology geek, is where did the air come from.

SAM KEAN: Yeah. It’s a question we don’t think about. It just seems like it’s always there. But–

IRA FLATOW: Why Is There Air was an album of– it was a few decades ago.

SAM KEAN: Yeah. So we’ve actually had on Earth, depending on how you count, about four distinct atmospheres in its history. There was a very early one. It was just sort of some wispy hydrogen and helium. Kind of a comb-over atmosphere that very quickly got blown away. Then there was a second atmosphere that came about from volcanoes that was mostly made up of really nasty gases– ammonia, hydrogen sulfide– the rotten egg smell– a lot of carbon dioxide. Very nasty. It wouldn’t have supported life. If you’d gone in a time machine, stepped out back then, and tried to take a deep breath, it would have just destroyed your lungs. So that was the second atmosphere.

And the third atmosphere actually came about from those same volcanoes. What happened was there was just a little tiny bit of nitrogen every time one of those volcanoes erupted. And over time, that nitrogen just built up very slowly, over billions of years. But eventually, you get enough nitrogen to kind of fill the atmosphere and be the dominant gas that we have today.

And then sort of a latecomer to this is oxygen, which didn’t start to accumulate until, you know, maybe a few hundred million years ago. It took a very long time for oxygen to build up to appreciable amounts in the air. And in fact, life on Earth predates oxygen by quite a ways. Oxygen was actually poisonous for most forms of life that existed on Earth through most of its history. And in fact, oxygen probably killed more organisms than any other substance in Earth’s history.

IRA FLATOW: So life had to evolve to use the oxygen?

SAM KEAN: To be able to utilize oxygen, because it’s so reactive that it was poisoning most of the early microbes that were around. The way I think about is sort of like a nuclear power plant, where you have plutonium in there. Plutonium is great. It’s very useful. A lot of energy there. But you have to keep your eye on the plutonium. You have to keep it confined. You can’t let it just kind of roam around and be floating around in a nuclear power plant. Same thing with oxygen inside microbes in cells. They have to keep it tightly confined. And they can only use it in certain places.

IRA FLATOW: They used to call it something else besides oxygen, didn’t they, early on?

SAM KEAN: They did. It was called phlogiston when they first invented it. It was a very great, old-fashioned name, phlogiston.

IRA FLATOW: What was it, just a Greek, Rome– what kind of word is it?

SAM KEAN: It was an idea back in the late 1700s, maybe a little before that, where they were trying to explain how substances burned. They really didn’t have an idea about the fact that there was something like oxygen that might exist. It was really coming out of the idea of burning things. And for a long time, they thought that just phlogiston existed. If you burned wood, burned a candle or something, it would be lighter afterward. The ash would be lighter. And so they thought, oh, OK, when something burns, this sort of mysterious phlogiston goes floating up into the air. And that’s how something burns is it releases this phlogiston.

IRA FLATOW: And somebody actually had to discover oxygen, right?

SAM KEAN: Yeah. There were actually a few different scientists that get credit for discovering it historically. A Swedish man named Carl Scheele, then an Englishman named Joseph Priestley, and then the latecomer who sort of horned in on this was Lavoisier, the very famous French scientist.

IRA FLATOW: There’s no one ever really first at anything in the world.

SAM KEAN: Yeah, I know. And unfortunately for them, oxygen turned out to be kind of a cursed discovery, in that all three of them met very, very bad ends.

IRA FLATOW: Wow. Wow. There’s a TV series there somewhere. We’re going to take a break and come back to talk lots more about air with Sam Kean, author of Caesar’s Last Breath– Decoding the Secrets of the Air Around Us. You can tweet us @scifri, S-C-I-F-R-I, with some questions, you’d like to comment. We’ll talk about it after the break. Don’t go away.

This is Science Friday. I’m Ira Flatow. We’re talking with Sam Kean, author of Caesar’s Last Breath– Decoding the Secrets of the Air Around Us. And as my engineer, Neal Rauch said, maybe we should really inhale, Caesar. Get it? Get it? See? He copyrighted that one already.


IRA FLATOW: If you’d like to tweet us, you can send it to @scifri, S-C-I-F-R-I. We have actually some questions that came in through the internet during the week, as we’ve talked about. Let’s go to one question first.

SPEAKER: Has the level of oxygen, the concentration of oxygen in our atmosphere changed over the last 50 years or so?

IRA FLATOW: That’s [INAUDIBLE] from Utah.

SAM KEAN: So, the level of oxygen in the air probably hasn’t changed over the last 50 years in any appreciable way. But if you look a little farther back, a few hundred million years, it definitely has kind of veered wildly up and down. And that has some interesting effects for planet Earth. When it’s in the low teens or the mid-teens, it’s very difficult to get fires going on Earth. So you actually don’t see any fires anywhere in the geological record of Earth until a few hundred million years ago, when oxygen finally built up to an appreciable level. So no fires back then.

And when it’s very high, you see some interesting effects on animals, especially, because insects, they have sort of this inefficient breathing process. They don’t have lungs the same way that a lot of other animals do. And as a result, they struggle to get oxygen to their interior cells. But if oxygen levels are a lot higher, insects can actually get much, much bigger. In the fossil record, you see millipedes that are a yard long. You see spiders the size of seagulls. You see these gigantic, gigantic insects just because the level of oxygen in the air was high enough to support them. So it does have some interesting effects.

IRA FLATOW: I have some interesting tweets coming in from Joy, who says thanks for the good cry. Learning I’m literally breathing the same air as my late father completely blew my mind.

SAM KEAN: Aw, yes. It does really connect you with everyone in your past, everyone you want to be connected with, yeah.

IRA FLATOW: Brandon writes in, and he says so the Earth’s atmosphere doesn’t replenish itself very often at all, if ever? Does this help support the CO2 is heating the earth?

SAM KEAN: Yeah, there is some recycling. So you know, nitrogen molecules might get brought in by nitrogen-fixing bacteria. Oxygen we obviously use in our metabolism, daily processes. But a lot of the molecules do stick around for quite a while in the air.

IRA FLATOW: Mhm. Is the air– did they evolve? Did they. Did the air and the water on Earth evolve basically at the same time?

SAM KEAN: Yeah, you see them both coming in very early in the Earth’s history.

IRA FLATOW: Are they connected? Do you know?

SAM KEAN: Yeah, there is some connections between them. Something like the carbon dioxide, which was really heavy component of the early atmospheres, sometimes that dissolves in the water, ends up becoming a mineral, something like that. So water can help regulate the levels of certain gases in the air. Or water vapor, when it goes up in the air, becomes one of the gases in the air. Water vapor is actually one of the big drivers of weather around the world. So there’s definitely an intimate connection between things like liquid water in the air.

IRA FLATOW: A lot of early chemistry involved scientists trying to figure out what effects different compounds had on humans. And one of them, which was very important, was you talk about as nitrous oxide.

SAM KEAN: Yeah, there’s actually little bits of nitrous oxide, little bits of– it’s laughing gas, basically– in the air all the time. And there was a lot of interest in the air because people back then believed that air caused diseases. So malaria literally means bad air. That was a theory about how diseases got spread. And a couple of scientists thought, well, you know, if bad air can cause diseases, maybe good air can cure diseases. So they were doing things like exposing patients to nitrous oxide, making them breathe it to see if they could cure consumption or palsies or other sort of old-fashioned diseases.

And what they figured out was that, OK, it maybe doesn’t work so well to cure these diseases, but there was a scientist named Humphry Davy who had a lot of friends, people like Samuel Taylor Coleridge, other poets, and they figured out, well, it has some interesting psychological effects here. So while Davy and his boss, a man named Thomas Beddoes, were running this clinic by day to try to help patients, expose them to gases, Humphry Davy and his friends would sort of sneak in at night and just inhale these gases, and basically get high, and try to figure out what psychological effects they were having.

IRA FLATOW: You know, your book has created a tweet storm. Talking with Sam Kean, author of Caesar’s Last Breath. Oliver wants to know, besides oxygen, do we need any of the other gases in the air to survive. You know, if levels of O2 and CO2 stayed constant, can other gas percentages change? What do we need?

SAM KEAN: Yeah, that’s an interesting question, actually, because we do need the oxygen. Without that, we just would not be able to live. It’s a question, though, with some of the other gases, because nitrogen, oxygen makes up 99% of the air, but they contribute zero to global warming. They don’t warm us at all. And actually, if it were only nitrogen and oxygen in the air, the average temperature of Earth would be a lot lower, something like 40, 60 degrees lower than it is.

So we need those other gases to increase the temperature of Earth to make it a little more comfortable. The problem, though, is that we’re increasing it enough where we’re sort of swinging past the comfortable level and pushing toward more extreme. So if we didn’t have all those other gases there, Earth would be a much colder place.

IRA FLATOW: A small section of your book delves into, how shall I put it, the bodily gases. What got you interested–

SAM KEAN: The gases we pass, yes.

IRA FLATOW: Gases that we pass, we burp, whatever, you know. What got you interested in that?

SAM KEAN: There was a man I read about named Joseph Pujol, who was a Frenchman. He was performing in the Moulin Rouge, late 1800s Paris. And basically, his act was to fart. He would inhale air through his rectum, and he would do impressions. Impressions of animals. He would sing songs this way. And he was actually the most popular act in the entire Moulin Rouge. The most popular, the most funny, the highest paid.

And it sounds a little low brow to talk about this, but you know, he had fans like Renoir, the painter, Ravel, the composer. Freud was a fan. The king of the Belgians once came incognito to see him. So a lot of highbrow, but some lowbrow in there, as well.

IRA FLATOW: So you could have easily entitled your book, instead of Caesar’s Last Breath, Caesar’s Last Fart.

SAM KEAN: Caesar’s Last Fart, yes.

IRA FLATOW: Because we’ve been inhaling that also.

SAM KEAN: Yeah, I mean, in some degree, we have been. It’s uncomfortable to think about, but those gases are in the air, as well.

IRA FLATOW: All right, speaking of smelly gases, we’ve got another caller wondering about the connection between the smell of substances and breathing them in.

REBECCA: Hi, this is Rebecca from Pleasant Grove, Utah. My question is, I wonder if sometimes when I smell something that’s toxic, like if someone put chemicals in my grass to fertilize it, can you smell it without breathing it in? Or if you’re smelling it, that means you’re breathing in something toxic? Or is the smell separate from the substance? Thank you.

IRA FLATOW: You’re welcome. Is that beyond your pay grade to answer that?

SAM KEAN: No. So if you’re smelling something, it’s getting into your body, obviously, getting into your nose. It might not necessarily get to your lungs, but it’s getting into your nose, at least. The question is whether the thing that you’re smelling is toxic, and whether the thing you’re smelling is harmful. So maybe you’re smelling part of it, but that’s not the toxic part, or there could be toxic things that you can’t smell. So it’s kind of a complicated question, but if you can smell it, it is getting your body, to at least some degree.

IRA FLATOW: So the air is mixing all the time, going in and up, up, up to the different atmospheres, up and down, and–


IRA FLATOW: Is it doing that all the time?

SAM KEAN: Yeah, it is mixing quite well. So the Caesar thing, you know, after he exhaled his last breath, it first sort of got spread at the same latitude as winds went around Earth, so at that latitude. But eventually, it spread out, smeared over the entire atmosphere. Probably in about two or three years, something like that.

IRA FLATOW: Mhm. You also include in the book– I’ve read a lot about Einstein, but I’ve never heard this story before about Einstein invented a new kind of refrigerator.

SAM KEAN: Yeah. We don’t think about him as a home appliances guru, but he also was very interested in gadgets like that. And I talk about it because, when you talk about refrigerators, basically gases are what’s driving refrigerators. They’re sucking the heat out of things, dumping it in another place.

And Einstein got interested because the gases that they were using back in the 1920s were usually toxic gases, things like methyl chloride, sulfur dioxide, ammonia. And it wasn’t uncommon for the seals to break on refrigerators and the toxic gases to leak out and to suffocate whole families in their apartment. You know, two, three children and their parents would die.

So Einstein called up a friend of his, Leo Szilard, and says, you know, there has to be a better way. So the two of them sat down, started tinkering, and actually invented three different types of refrigerators, which Einstein was very happy about. He thought it was going to make him some money. He was in kind of dire circumstances at the time, living in Germany during a time of hyperinflation. He had just remarried. He had two families to support. So he was pretty excited about the prospects for these new types of refrigerators that he and Szilard invented.

IRA FLATOW: Speaking of the air in our atmosphere, couple of questions. Why do we still have air and, let’s say, Mars doesn’t have air?

SAM KEAN: Yeah. Mars is a little smaller, and for various reasons Mars doesn’t have the gravity to hold on as well. Mars also lacks a magnetic field in the way that Earth did. So– the Earth has. So Earth, because of that magnetic field, when you see particles streaming in from space, that magnetic field helps deflect those particles, push them away, whereas Mars, lacking a magnetic field, those particles ram right into it. And they can help push the gases away. So Mars does have a vague atmosphere, but not a strong one like us.

IRA FLATOW: So may have had that same kind of gasification early on, but it just couldn’t hold on.

SAM KEAN: Yeah, exactly. Mars almost certainly did have a similar to our early Earth atmosphere.

IRA FLATOW: You also talk about something that is very, very important to the history of industry. And that is our understanding of steam, which is a gas.

SAM KEAN: Steam is a gas, yeah, the gaseous form of water. And steam was really the big driver of the Industrial Revolution. In fact, there were lots of different gases involved with things like explosives. Steel creation relied on gases. But steam was one of the big, big ones.

And James Watt is the one usually associated with that. But it was really learning how to harness the power of steam, how to harness the power of this gas, and direct it, because gases are very powerful. They can do a lot of work. But again, you have to confine them, harness them. And Watt and his partners were the one who really figured out how to do that.

IRA FLATOW: Mhm. Even in more modern times, humans have had a very complicated relationship with gases. And I’m thinking about the same person who created nitrogen from the air, who found a way to take the nitrogen to create fertilizer to feed millions also created the chemical weapons for the kaiser in World War I.

SAM KEAN: Yeah. The man involved here is a Fritz Haber, who a very, very complicated–

IRA FLATOW: The Haber Process.

SAM KEAN: The Haber Process, yeah, very, very complicated. So nitrogen, you know, it’s very important to us. We have nitrogen in every protein, every DNA strand in our body. And there’s a lot of nitrogen in the air. The problem is that that nitrogen in the air isn’t a useful form. We can’t inhale that, and our bodies can’t use it. You have to turn that nitrogen into something like fertilizer, get it into plants, then we can eat the plants.

And Haber was the one who figured out how to take that nitrogen out of the air, make it into a substance, ammonia, that then you could turn into a fertilizer. And it’s not much exaggeration to say that’s probably the most important chemical process that human beings have ever discovered. Half of the human beings on Earth would not be here today without that process. It is a vitally important process for modern civilization. And Haber was rightly hailed at the time as one of the great benefactors of humankind.

Unfortunately for him, he also was an ardent German patriot. And when World War I came around about half a decade or a decade after this discovery, he turned all his chemical genius over to the idea of making gases that we could use in warfare. And he was really the one who turned gas warfare into the deadly, awful thing that we think of today.

So on the one hand, he was a great benefactor of humankind. On the other hand, he did these awful, terrible things, terrorized millions and millions of soldiers during World War I. And you even see right after the war he won a Nobel Prize for the Haber Process, but was also condemned as an international war criminal almost at the same time. So even back then, people had this very contradictory view of him.

IRA FLATOW: Very interesting portrait of him in the series Genius about Albert Einstein. He’s a figure in that series.

SAM KEAN: Yeah, he knew Einstein. In fact, when Einstein was having some trouble with his family, Haber was the one who came and comforted him. They were close, in a way.

IRA FLATOW: Yeah. This is Science Friday from PRI, Public Radio International. Talking with Sam Kean, author of Caesar’s Last Breath. Really, really interesting book. It’s a page-turner. I mean, if a science book could be a page-turner. And you start out by just talking about air, but you go into all this interesting chemistry that’s involved with oxides, I guess because oxides are part of air.

SAM KEAN: Yeah. It’s fun to be able to start with something like the air, and then to jump into so many different areas and talk about things like warfare, volcanoes, talk about anesthesia, talk– there’s a little bit about aliens in there. There’s a lot of different places you can go with the air if you kind of know how to decode and interpret those stories that are sort of flitting invisibly around in front of us all the time.

IRA FLATOW: And you know, that’s an interesting way to teach science. In fact, we have a tweet from David Finney, who says idea like that makes kids think. Create a connection to history. Keep it up. That we are all forged in stars is so powerful.

SAM KEAN: Yeah. It’s a way to get people’s attention, and to help them remember the science, too, because when you do science in story form, which is what I’m really trying to do in this book, it’s easy to remember that in a way it isn’t easy to remember sort of disconnected facts. If there are heroes, villains, conflicts, our brains are very good about remembering and absorbing it when it’s presented that way.

IRA FLATOW: Because people don’t actually think about scientists as people.

SAM KEAN: Yeah, they’re sort of these abstract robots that just– they take in coffee, and they spew out discoveries. That’s what scientists do. But you know, they are humans. They have the same motivations that all of us do.

IRA FLATOW: You think? Anything coming up? Anything to follow this book? You working on something new, or?

SAM KEAN: Yeah, we’re throwing around some ideas with my editors right now. But right at this point, really focused on the book. I’ll be speaking at a lot of different places around the country. So you can go on my website, find out some more information about that.

IRA FLATOW: Which is?

SAM KEAN: Which is SamKean.com, so just S-A-M-K-E-A-N dot com.

IRA FLATOW: What made you decide on this topic? Why air?

SAM KEAN: Because it’s such an important topic right now. A lot of controversy about it, lot of questions about what the future of air will be. So I thought, you know, if we know the past, the history of air, all these rich, rich stories about it, it will help us understand where air is going in the future, too.

IRA FLATOW: The air, the air is everywhere. Where is that from?

SAM KEAN: The air, the air is everywhere? I don’t know.


SAM KEAN: I think of the–


SAM KEAN: –water, water everywhere, not a drop to drink.

IRA FLATOW: The air, the air is everywhere. Thank you, Sam.

SAM KEAN: Thank you for having me.

IRA FLATOW: It’s a great book. The book– I’ll read the whole title, because–

SAM KEAN: All right, take a breath.

IRA FLATOW: It’s a book– very good. Sam Kean, author of Caesar’s Last Breath– Decoding the Secrets of the Air Around Us. And to read an excerpt from the new book, you can head to ScienceFriday.com/gases.

BJ Leiderman composed our theme music, and we had engineering help today from Neal Rauch and [INAUDIBLE]. Thanks to all the folks at NPR for help this week. If you’d like to write us, send your letters to Science Friday, 19 West 44th Street, Room 412, New York, New York, 10036. You can also go to our website at sciencefriday.com. And every day is Science Friday on social communities. We’re up tweeting and Facebook and all over the place in social communities. We’re very happy to have you as a member.

I’m Ira Flatow in New York.

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