And in fact, life on Earth predates oxygen by quite a ways. It took a very long time for oxygen to build up to appreciable amounts in the air. But eventually, you get enough nitrogen to kind of fill the atmosphere and be the dominant gas that we have today.Īnd 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. And over time, that nitrogen just built up very slowly, over billions of years. What happened was there was just a little tiny bit of nitrogen every time one of those volcanoes erupted. So that was the second atmosphere.Īnd the third atmosphere actually came about from those same volcanoes. 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. 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. Kind of a comb-over atmosphere that very quickly got blown away. It was just sort of some wispy hydrogen and helium. So we’ve actually had on Earth, depending on how you count, about four distinct atmospheres in its history. ![]() IRA FLATOW: Why Is There Air was an album of– it was a few decades ago. 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. Talking with Sam Kean about his new book Caesar’s Last Breath. This is Science Friday from PRI, Public Radio International. So once nitrogen gets in the air, it stays around for a very long time, usually. Two atoms of nitrogen with a triple bond between them, very, very stable, very hardy. Sticks around for millions, maybe even billions of years. But nitrogen is a very, very hardy molecule. A lot of the components of the air are reactive. SAM KEAN: It’s mostly the nitrogen in the air. IRA FLATOW: Why does the air last that long? SAM KEAN: And there’s lots more left over, because there’s seven billion of us, there’s 25 sextillion molecules. IRA FLATOW: And that would be a molecule, then, for everybody in the world. 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. 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. Very small.īut 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. It’s something like 19 zeros with a one after them. One is how small an individual breath seems compared to the atmosphere. SAM KEAN: Yeah, there’s kind of two forces working against each other here. 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? IRA FLATOW: Let’s get the heavy math out of the way first here. ![]() The way you talk about air, I mean, you have a great talent for writing. And not just the human past, but Earth’s geological history, as well.Īnd 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. 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. And that’s because many of the molecules that make up our air, like nitrogen, are surprisingly hardy. ![]() How could I be inhaling those same air particles? There’s no possible way there should be anything left.īut as you’ll soon hear, the math that we’re talking about does check out. I know what you’re going to say, it’s just one breath expelled over 2,000 years ago. 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.
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