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ANDREA SEABROOK, host:

Time for a quick break. Now, take a deep breath in…

(Soundbite of breathing in)

SEABROOK: …out.

(Soundbite of breathing out)

SEABROOK: You need air to survive. But have you ever really thought about what's in it?

(Soundbite of music)

SEABROOK: This week, we're really taking our Science Out of the Box - actually, out of the building.

Okay. I'm sitting out on the rooftop deck of NPR now. And joining me to talk about what's all around us is Gabrielle Walker. She's the author of "An Ocean of Air."

Gabrielle, where are you?

Dr. GABRIELLE WALKER (Author, "An Ocean of Air"): I'm sitting in a rather nice green park in the middle of London.

SEABROOK: What do you see all around you?

Dr. WALKER: Well, before I started writing this book, I'd look around me and I'd say when I'm in the park, I see animals and people and some plants and trees. But after writing it, much to my surprise, what I see around me, everywhere is the influence of air. I used to think that the air was just about breathing. But in fact, all these animals and people - there will be no life on Earth bigger than a pinhead if it weren't for the nature of air. I'm also looking up and seeing lots of clouds and hoping it's not going to rain on me.

(Soundbite of laughter)

SEABROOK: It's a kind of a sad hope in London.

(Soundbite of laughter)

SEABROOK: Gabrielle Walker, even the title of your book, "An Ocean of Air," it sort of evokes the fact that it's not nothing that's all around us here in the world. It's something.

Dr. WALKER: I think that's actually why I wanted to write this book in the first place. Because I was reading about a wonderful scientist who was a disciple of the great Galileo. And he's the person who first figured out how heavy air is. And I knew that air was all around me. You know, we often don't notice it and so on. But I haven't realized just how heavy it is. If you think about the Carnegie Hall and you (unintelligible) older people and everything, you just leave air in it. You kind of think just how heavy might that air be. And it's amazing, it's actually 70,000 pounds. And where do you get…

SEABROOK: Wow.

Dr. WALKER: And so what Tony Kelly(ph) did, when he weighs the air. He figured out how heavy it was, he wrote this one particularly romantic thing. He wasn't really that romantic a writer. He was a bit a scientist in the way that he wrote. But he wrote a letter to a friend. He said we live submersed at the bottom of an ocean of air.

You know, I'd spent my life thinking I was walking around on a surface of a planet. I didn't know it was at the bottom of an ocean. I felt like, you know, it's something (unintelligible) I was a lobster and I was looking at all those things that are on ahead of me and (unintelligible) and I didn't even know.

SEABROOK: Now, it's interesting because here, you know, we've just had a helicopter go over here. And, you know, once in a while, you do look up and you think the helicopter is actually moving through something. I mean, there's something that's holding it up in much the same way that a fish swims through the ocean.

Dr. WALKER: Right. And so it actually turns out to be a really good analogy. It has different layers. It has currents, what we call the wind but were just like currents under the ocean. And it really has substance so things can fly in it. But, you know, the other thing that I really loved when I was investigating about the air is that the bottom-most part of it, the bit that we live in and breathe in and brings us all our weather, that's the really sick part, and that's the part that transforms the Earth. That's the part that gives all of these dogs and animals and plants and everything. I'm seeing (unintelligible) right now in this park. But there's other part - so as soon as you get higher up, we have layers that don't transform. Those are layers that protect.

And I'd always thought that air was really fragile. You know what I mean? The astronauts - those went up into space - and saw this thin blue line and, oh, it's so beautiful. Oh, it's so fragile. But in fact, it's incredibly strong. And those three layers, the ozone layer, the ionosphere - it's called the magnetosphere - when you put them together, they protect us from the most hostile and extraordinary attacks on space. And they're so good at it that we don't even notice.

SEABROOK: Right now, we're hearing sirens go by hear in Washington. And, you know, that happens all the time here, as a motorcade passes by to take a different dignitary every 10 minutes. But the siren is actually - I mean, I sound is moving through something again. I mean, sound doesn't travel in a vacuum, for example. So it's actually using the air to travel through. Isn't that right?

Dr. WALKER: That's absolutely right. It's another of those precious things that air brings us. If there were no air - and assuming you could still breathe and survive - a cannon could go off next to you and you wouldn't hear a thing. The air actually has to take the sound and transfer it. Otherwise, you couldn't hear it. And you wouldn't even feel it. You know, if an explosion goes off, you get thrown off your feet. And the reason is that the explosion hits the air, which hits other part of air, which hits you and knocks you. And as you think about that, and you think about the way a strong wind can take the roof off a house, it's really powerful stuff.

SEABROOK: And not only do we have that special relationship here at NPR with sound, but also with radio. And how does air affect that?

Dr. WALKER: Radio waves don't actually need air to move through. But there is something special that one of the protective layers does. And that's often the ionosphere. That's the place where you see the northern and southern lights, the Aurora Borealis. And that's also the place where you see meteors, shootings stars. And they shoot in and they deposit their layers of ion and metal. And you got this kind of layer of metal almost like a shiny mirror up in the sky.

And it's also incredibly electric. You have this fantastic huge currents of electricity that crackle their way around us in strange glowing globs of electricity. And that's the layer that radio waves bounce off.

So even before we have satellites, that's how radio waves could bounce up into the sky and back over the horizon. That's how radio waves made it from the Titanic, as it was sinking, to the ship that was over the horizon that came steaming along to save the survivors.

SEABROOK: Gabrielle Walker, you've given us a new appreciation of air. Thank you so much.

Dr. WALKER: Oh, my pleasure.

SEABROOK: Gabrielle Walker is the author of "An Ocean of Air." She joined us from a park in London while we sat here on the roof deck of NPR in Washington, D.C.

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